It's a forum where taking atheism for granted is widespread, and the 10% of non-atheists have some idea of what the 90% are thinking. Being atheist isn't part of the official charter, but you can make a function call to atheism without being questioned by either the 10% or the 90% because everyone knows where you're coming from. If I was on a 90% Mormon forum which theoretically wasn't about Mormonism but occasionally contained posters making function calls to Mormon theology without further justification, I would not walk in and expect to be able to make atheist function calls without being questioned on it. If I did, I wouldn't be surprised to be downvoted to oblivion if that forum had a downvoting function. This isn't groupthink; it's standard logical courtesy. When you know perfectly well that a supermajority of the people around you believe X, it's not just silly but logically rude to ask them to take Y as a premise without defending it. I would owe this hypothetical 90%-Mormon forum more acknowledgement of their prior beliefs than that.

I regard all of this as common sense.

I don't believe that rationality in general is incompatible with religious belief, but if this community thinks that their particular brand of rationality is, people like me would love to know that.

Might we not, instead, disagree with you about rationality in general being compatible with religious belief, rather than asserting that we have some special incompatible brand of rationality?

I think it that most of your problems with theists would go away if you clarified LW's actual position.

Do we really have "problems with theists"...?

The comment above from EY is over-broad in calling this an "atheist forum", but I think it still has a good point:

It's logically rude to go to a place where the vast majority of people believe X=34, and you say "No, actually X=87, but I won't accept any discussion on the matter." To act that way is to treat disagreement like a shameful thing, best not brought up in polite company, and that's as clear an example of logical rudeness as I can think of.

This is not an atheist forum, in much the same way that it is not an a-unicorn-ist forum. Not because we do not hold a consistent position on the existence of unicorns, but because the issue itself is not worth discussing. The data has spoken, and there is no reason to believe in them. Whatever. Let's move on to more important things like anthropics and the meta-ethics of Friendly AI.

You are fixating on atheism for some reason. Assigning low probability to any particular religion, and only a marginally higher probability to some supernatural creator still actively shaping the universe results naturally from rationally considering the issue and evaluating the probabilities. So do many other conclusions. This reminds me of the creationists picking a fight against evolution, whereas they could have picked a fight against Copernicanism, the way flat earthers do.

If people have a problem with it, that's not my fault.

It might or it might not be. As a general rule, if two people think that a single issue of fact is a settled question, in different directions, then either they have access to different information, or one or both of them is incorrect.

If the former is the case, then they can share their information, after which either they will agree, or one or both will be incorrect.

If we're incorrect about religion being a settled question, we want to know that, so we can change our minds. If Mormonism is incorrect, do you want to know that?