I'm an atheist, also an ex-Christian.
"Atheist" is the state I was initially born into; while "ex-Christian" is the identity I have obtained after an extensive period of believing in Christianity and the de-conversion from it.
Atheists can have a lot of variety among their groups. Just like there are differences among Christian groups, their associated religions and branches, just like how a Christian is different from another Christian living next door, there are differences among atheists, too. In the window I introduce below, I'll categorize atheists into four groups by indicating their friendliness to religious people and their motivation to share their views to religious people. The number of atheists in each group is determined by the tendencies they have.
The unfriendly atheists
On the left side of the window, we have atheists who have low friendliness to Christians and religious groups. They can be further differentiated into two groups: the first with high motivation to reason with Christians; the second having a low motivation to argue with Christians. With low friendliness, these atheists can be sarcastic comedians who often mock Christians (the mockers). Even though I tend to agree with their views, I'm glad that many of them keep their jokes among their social circles (the treaty-signers). Otherwise, religious people would be offended and be turned away frequently. Although some of the worldviews of Christians can be very radical, violent and offensive to us as well, I'm not here to discuss right or wrong but looking at the problem from the perspective of effectively "preaching" atheism to these people. Mocking Christians simply will not shake their beliefs because no one is willing to join any group which is unfriendly to them.
The atheists who do not bother
In reality, however, atheists are not always poking fun at Christians and being sarcastic to them because they know when to give up reasoning with Christians - some of them may become frustrated after discussing with Christians and conclude that "Christians are stubborn". As a result, the number of atheists with low motivation to share their worldviews with religious people rises. The group of atheists who actively argue with Christians may fall back into two low-motivational groups. They either keep their atheism mute to Christians but to continue their mocking among their social circle, concluding how Christians are illogical, irrational and impossible to reason with, or they do so with the consideration of politeness and friendliness. Here comes the third group of atheists in the window -- the peacemakers. They don't actively make attempts to change Christians' views as Christians would try to change theirs; they don't share their own views with Christians; but they're very friendly people who insist not imposing their views on others.
The "preaching" atheists
The fourth group of atheists are with high friendliness and high motivation to share their views with religious people. These are the people who invite Jehovah's Witnesses into their houses and serve them with milk, and, most importantly of all, talk to them for hours on religious matters. Some of them can be very successful in persuasion. When Richard Dawkins or Christopher Hitchens is invited to a Christian university for a debate, he is presenting logical arguments for the critical mass. Sharing our views with Christians when they aren't ready, however, can be slightly but intriguingly different. Nevertheless, talking to people who share a different viewpoint from us in an interpersonal setting can be a skill to be acquired from trials-and-errors. Merely exercising our freedom of speech doesn't mean that everyone will be convinced. This is when the term "persuasion" or "preaching" comes into play.
This article is intended for those who are interested to explore how some of the atheistic arguments can be effectively presented to Christians without backfire, the psychology of preaching and conversational skills but it is no magic bullet either. It may inspire you to think more about the art of talking to Christians if you are aiming to help them as an atheist. I do hope more and more atheists will eventually grow into the fourth type - willing to share their views in a friendly, patient manner. Since being an atheist means recognizing the right set of morality and making an effort to understand the world and oneself, we ought to share what we have with the others. Just like religious people are passionately preaching for their gods with their scriptures, guiding (and misguiding) the mass towards their churches and temples of their gods, we should let the world know what's inside our heads, too. Joy may not be sparked instantly but your effort will be appreciated by those who discover its value.
The first thing is empathy
So how do we talk to evangelical Christians when they approach us? The most essential thing is the correct attitude. We need to have empathy for Christians, which means trying to understanding why a person who has been converted to Christianity would have made such a decision. I remember, many years ago, when I was still an evangelical Christian, how my atheist friend accused me of trying to impress God when I was preaching to her. Such a move was disrespectful, impolite and even insulting to me as I was genuinely worrying that she would be sent to hell if she got it wrong. In terms of the de-converting process, it was not effective at all. Thus, the first point to start with: we should attack the arguments whenever necessary, but not the people having certain religious beliefs, unless you know for certain that they are scammers. This could be hard if you have not gone through the paths Christians have gone through but you could think about how you would like to be treated as a human being as a guiding principle. Christians may be misguided and gullible in many ways but they, as human beings, can also experience frustration like atheists do when a dialogue is not taking anyone anywhere.
The next step is to do an inquiry for the training most beginner evangelical Christians have gone through. Then, we can summarize the attributes these evangelical Christians share. The typical beginner courses offered by churches equip Christians with basic logical arguments and formulated responses; meanwhile, there's some psychology behind the study and the practice of preaching. Below I will list out some of the characteristics you may spot in a discussion with beginner evangelical Christians and devise how we can deliver atheistic thoughts economically.
Ruling out dichotomy
When Christians approach you in the street, what comes with them may actually be more than their arguments. They carry with them their assigned identity as servants of God; they also have certain expectations on you; they have set certain goals for the conversation to come. When you introduce yourself as an atheist, you could consider falsifying the stereotype that many Christians have on us so as to rule out dichotomous thinking for both you and the preaching Christians. For me, I may tell them that my morality is partly based on universal values and partly shaped by my former Christian thinking. For example, a human being making sacrifice for another human being -- a Samaritan act -- should be glorified as an act out of ultimate care.
When reasons meet blind faith
Don't worry about bringing up atheism with Christians as they would take the initiative to reason with you. By "reason", I mean they will bring up gospel -- define concepts of sin and Jesus as the bridge between men and God as well as how God was originally your father-in-charge and explain why we must accept the "gift" from the Christian God or be expected to be sent to hell. Many atheists consider gospel as fairy tales but even fairy tales have their plots built within, with that we can evaluate whether the story told is logical, and whether the resolution is acceptable, or not.
With a stage set up by Christians for logical arguments to meet, we could guide them to reason with common sense. We may start by pointing out how we cannot accept Christian justice brought by the New Testament, that even a violent child rapist can just walk away from court and spend time with the child he had brutally raped in paradise if he lets the judge beat up his own son and accepts such "gift"; that we cannot accept a good person who did NOT brutally rape a child being sent to eternal torture merely because they want to take responsibility for their mistakes in life. Ask Christians this question when they present to you their "free-gift booklets": if they can't accept such a judicial system in our courts, how can they accept the very same system offered by Christianity?
Dealing with subjective experiences
Another common strategy employed by Christians is the appeal to subjective experiences: no one can know the taste of a candy unless they put it into their mouth and taste it! Life is full of interesting experiences; we can often assign meanings to it and set self-actualizing goals for ourselves. So try not to question someone's subjective experiences unless a belief is so harmful that it is putting someone at risk. Even atheists occasionally figure out some meaning in life by seeking and creating purposes based on people we care rather than reading a holy book written or given by some supreme beings. So, again, it is not the subjective experiences that we should question but the attribution of these experiences to the Christian God that is problematic. In this case, a simple, direct question is enough: how did you know that was the Christian God, not your great grandmother watching you in the sky?
For some atheists, this is a bad move as it may reinforce another claim that lacks evidence but if you look at the abductive reasoning behind the question, it could open up more gateways for the listeners and become the first step of nurturing the free-thinkers within Christians. As we think about it, Christianity borrowed the term "father" and coined the term "heavenly father" as a substitute of "God" or "Lord" so that people can associate the love, care, awe and all their personal experiences since they had been born with the concept of the creator. Bringing up the great grandmother who might still be in the sky, you may guide them to compare her, a person who had lived and deceased, who has real kinship with the listener, to the concept of God. Meanwhile, you are re-assigning the root of the subjective experiences to a more plausible cause -- family, and let them re-experience it from within. When you were a baby, before you could voice out "mama" properly, before you could recognize her, your mum has been taking care of you. Her love for you is simply that unconditional. Now that you're calling Jesus, a complete stranger who was born 2000+ years ago, and his "heavenly father" as your own dad, your great grandmother could still be watching you from another world and taking care of you because you are a miracle to her. The goal of this narrative is to help Christians to consider alternative, feasible possibilities when presented with one single claim by religious authority.
Pointing out fallacy
A rather covert but resilient technique used by Christians is presupposition. The so-called omni-perfection of the concept of "God" and how he cares for everyone of us, how he is more superior as a creator to everything in life, etc. gives a preacher limitless imaginary authority to bring him up in a conversation. All the narratives of God could be considered as a paradigm only if he wasn't just one of the concepts people made up. Try not to challenge Christians too directly but point out to them the fact that people born in different cultural and religious zones tend to have their unique understanding for the very same word. Hence, while someone is making certain assumptions on their God, someone else on the other side of the globe is rightfully making very different or even opposite assertions on their God(s) as well.
On an emotional level, Christians can be very kind people (though some of them can also be condescending) when they bring their gospel upon us. They fear for their scripture tells them the acceptance of the Christian God is the only way to escape his eternal torture. For the same reason, they consider themselves as the paramedics who have an urgent task assigned by the holy of the holy who has also set up the whole game of either-accept-me-or-die. This identity not only gives them something to celebrate if they get a positive response but also leads them to disappointment if they get a negative reception. Either way, their inclination to preach is reinforced.
Make your stance clear
To deal with the paradox of reinforcement, make sure you do not say a prayer with them out of empathy or rapport. Then, explain that no one is going to hell for small mistakes they are making in life. Let them know that no one deserves to be treated like a mass murderer if they aren't one themselves. Bear in mind that it is neither reason nor sentiment alone that drives someone to sacrifice their free time to knock on your door or approach you with shyness in the street. A combination of conditioning, manipulation of emotional state and cultivation of the mind was done to these originally rational people. An equal amount of time and patience ought to be spent on them if you take deprogramming as a goal.
What's the mysterious plan?
Finally, in a typical preaching conversation, in case everything fails, Christians had been taught to fall back to a self-deceiving trick. They will humbly tell you that they were not trained to answer your clever questions yet and that they'll need some more time to be enlightened by God and his truth -- a statement that assumes the validity of their beliefs without objective support. They are likely to add that God has a plan for you, too.
For many atheists, this can be a condescending move but if you're kind and patient enough, you may also take the chance to wrap up the conversation by blessing them for one day they may find the truth themselves. Elaborate how the churches have schemes for their followers. For example, the lectures provided by churches defending Christianity will never reveal all the strong arguments presented by atheists, former believers and former pastors. They would even accuse former believers as people who were never really chosen by God. In order to catch a glimpse of logical arguments from both churches and atheist groups, invite them to do their own research on YouTube; watch a debate session or read a book that'll upset a church. Bless them to walk on a path that they could dig up.
This endnote is not a prayer
If you're an atheist and you're reading this, I sincerely give thanks to you for your patience, for you care for your humankind who stumbles into worlds of fantasies because of their overly stimulated prefrontal cortexes, who has the human tendency to be deceived by the stories circulated by their misguided peers, who self-deceives due to pride and prejudice and the reluctance to face their own mistakes, mistakes they made in reasoning and mistakes they made in life. I'm sure Christians will, one day, thank you for your reading their Bible not because you play along with it and say a prayer but for your willingness to let them know why it deserves a low rating. A-men.