It's very easy to say if your family rejects you, it rejects you, and you "simply" move on. But particularly for a young person, that's way easier said than done, particularly if their family and maybe their church is their sole source of social support.

The young often don't have a very firm "center" and lack the confidence to assert themselves, particularly with someone as symbolically important as a parent.

The young are also often semi-financially dependent on their parents / immediate family to get through school and sometimes the initial years of getting established in adult life -- thanks to the ridiculous expenses and exploitive debts involved with higher education, and the shifting dynamics of entering a shrinking middle class. So they literally cannot AFFORD to honk off their parents, especially in such a primal manner.

I often counsel young people to suck it up at least until they have a good stable income source, are done with school, not excessively in debt, and have their own social support system. It's not THAT big a deal to sit through a church service now and then to humor your family; it's not going to last forever.

After all people are going to encounter this kind of shit throughout life. The employer who can't handle the truth: I don't let my clients know my personal beliefs, I don't want it to bring my trustworthiness and motives into question. It's not worth the risk to give them TMI that's not really their business anyway. The neighbor who can't handle the truth: no one in my neighborhood has the slightest idea what my metaphysical beliefs are, beyond perhaps noticing our car generally remains in the driveway on Sunday mornings (not that unusual around here anyway). And so forth.

I don't think "coming out" as atheist is anywhere near in the same league as "coming out" as gay or trans or something. My atheism doesn't prevent me from living according to my fairly conventional ethical code or behavioral norms. I wouldn't live any differently "out" vs "not out" as atheist. On the other hand my sexual preferences, if I had to repress them, would limit who I could be seen as close to, how I express affection publically, etc. So if I were gay or trans I'd pay a heavy price for being "not out" (or, sadly, for being "out" ). And it is much more of a dillemma. I think we atheists sometimes unintentionally insult our LGBTQ friends by talking about whether or not we should "come out".

This type of question gets asked often on this forum and I am always curious about it because this subject NEVER comes up in my family interactions. And I have no idea why or how it would ever come up in a school, at least in any public school setting. People say "coming out as an atheist" like people used to say, "coming out as gay," as though it were shocking or shameful. Tell someone you are an atheist, and then if they want to pursue it, tell them you don't want to continue to talk about it. Then if they continue to pursue it, you can change the subject or LEAVE. I find the swift departure gives them a pretty good idea of how successful any future such attempts would be.

You're american so it's obvious that you ask this kind of question.

I guess there is a balance between making the rational choice of being fake but not having to deal with unnecessary consequences of being kicked out of the house, marginalized, bullied etc (depends on family)

...or doing the morally right thing to not lie and not be fake.

I guess it can vary greatly from each person's situation... but personally I don't have too much faith in parents in general. Most parents don't seem to be understanding/open minded. Most parents seem to think that they should control their kids like slaves with an iron fist and if a kid ever talks back, he is an ungrateful brat. Girls tend to get the better end of the deal. But again it depends on each person...