My suggested resolution is as follows:

1) "Don't ask and for God's sake don't tell." This is a group where people come to speak freely about rationality. If you don't talk about your beliefs about God, no one will press you on it or demand that you affirm anything.

2) However, part of our zeitgeist is that it's okay to question beliefs, or even try your hardest to destroy beliefs you think are false, because that which can be destroyed by the truth should be. There are no exceptions for anything, and if you say anything indicating that you think religious beliefs should be exempt, people are not going to nod along, instead they are going to start talking about "The rule that you have to look at a city in order to draw an accurate map of it has no exceptions".

3) Criticism of religion is not taboo - it goes against both the ideals of rationality we believe in, and the atmosphere of freedom that draws us to the group, to have that sort of taboo for that reason. So, to put it bluntly, you will overhear other people comparing belief in God to the Tooth Fairy, and if you contradict them they will contradict you back, and if you say that everyone has a right to their own opinion they will start trying to explain to you the concept of "anti-epistemology".

4) Atheism might not be mandatory inside a rationalist community - but what is mandatory is the idea that it's allowed to argue beliefs, and that attacking the belief isn't the same as attacking the person. And if you decide that you're offended, you will not get sympathy or agreement on that point from the group, because the idiom of "I Am Offended, Shut Up" is something we have explicitly decided to give up.

5) Atheists are obliged to argue carefully with theists, and hold their arguments contradicting theism to the same sort of skeptical standard that they would use for arguments in favor of a dislikable conclusion instead of a likable one. If you, say, claim that "Time didn't exist before the Big Bang" is a complete and satisfactory solution to the problem "Why does something exist instead of nothing?", rather than (as is the correct answer) trying to explain why saying "God" (a) doesn't help and (b) constitutes the cardinal sin of Just Making Stuff Up, then you have lost all claim to any moral victory. (This last point is really a more general one, but it is an example of the sort of respect that you do owe to a religious newcomer, and if you deny them that respect - if they see that you are allowed to throw bad arguments at them that you wouldn't throw at anyone else - they are quite justified in walking away in a huff.)

6) Don't sweat losing some possible recruits. There's enough atheists in the world, or theists who can tolerate disrespect for theism, that in the present stage of the community's growth it is definitely not worth compromising community values of rationality in order to hang onto people who still have a sense of entitlement to their Offense.