A community of HPMOR!Quirrell variations would have your very post in main, with plenty of upvotes, all the while secretly whetting their blades. Perfectly rational.

I really don't think so. A community of Briennes, which is not a community of HPMOR!Quirrells but shares some relevant features, would recognize the overwhelming benefit of coordination. Any given individual would be much stronger if she had the knowledge of all the other individuals, or if she could count on them as external memory. And because she would be stronger that way, she knows that they would be stronger if she also remains trustworthy. Her being trustworthy allows her to derive greater benefit from the rest of the community. Other people are useful, you see. With Tell culture in place, you can do things like feed your model of the world into someone else's truth-checker and get back a more info-rich version. You only defect if the expected utility of doing so outweighs the expected utility of the entire community to your future plans.

I'd love to hear what culture Eliezer thinks an entire community of Quirrells would create.