I don't think such a site would collapse. Instead, it would fragment into different bubbles, some of which would be toxic to mainstream users, but users wouldn't see any of that toxicity without specifically opting in to it.

I imagine such a platform would turn out like Reddit, only better, since people who opt out of the consensus reality would probably have their messages only visible to like-minded users, unlike on Reddit where each user is trusted by default in each subreddit.