Also, don't forget that you don't belong to one community; it's not like you log in one day and get assigned to your immutable chunk of the internet. You wander around the read versions of various communities, pick a couple of communities you invest it, pick several more to half-follow, get tired of the abuse in one and switch to another, meet someone in real life who encourages you to join another community, and so on.

Basically, the sort of "tribalism" that you'd encounter is whatever "tribalism" you associate with HN, because the structure I describe already half-exists, scrounging around the remnants from reddit and Facebook in tens of thousands of forums and active blogs and other such things. I don't think it produces any more or less "tribalism" than you get from anything else.