Correct me if I'm wrong, but it looks like you're talking about anti-deathism (weak or strong) as if it was a defining value of the LessWrong community. This bothers me.

Well, it depends what you mean by "defining value". The LW community includes all sorts of stuff that simply becomes much more convincing/obvious/likely when you're, well, more rational. Atheism, polyamory, cryonics ... there's quite a few of these beliefs floating around. That seems like it's as it should be; if rationality didn't cause you to change your beliefs, it would be meaningless, and if those beliefs weren't better correlated with reality, it would be useless.