Well, firstly, the ability to make rationally optimal decisions is not merely a matter of cultural preference. Promoting the ability to make decisions which marginalize errors generally - under
arbitrary goals - does not inhibit anyone from having a satisfying culture. Rationalism doesn't choose your goals, it determines the optimal way to achieve them. Now, it
does inhibit people from participating in a culture which promotes their death as some 'ideal' state of being, as most religions that promote an idyllic afterlife do.
I mean, if you put me on a raft out in the ocean and ask me whether we should shoot and eat the Christian or the Atheist, I'm going to ask "which one of them asserts their death will result in a state of unending glory and euphoria while preserving the 'existence' of their mental state?" Because that's the one that should be killed. And these kinds of biases pile up over the long term, leaving a distinct mark of fragility and unnecessary risk on the entire culture. You have ability to choose that, but I cannot advocate that you ever should.
Secondly, it is not a historical accident that this issue has been decided by force. It is not even really true; far more violence has been carried out in the name of spreading religion than has been in the name of eliminating it. And again, this is of little relevance anyway, because the past has been more violent in general, and we have better understood and more widely available means of achieving goals through peace today than any time in human history.