I've seen something similar referred to as the "Voat" effect. Voat was a reddit alternative that popped up when reddit started banning subs that had poor optics (the explicit hate subreddits, the pro-racism subreddits, the basically-child-porn subs). Voat was founded on a principle of free speech, allowing whatever content users wanted.

Regardless of whether reddit made the correct decision banning those suspect subreddits, it turns out having a community composed almost entirely of those cast-offs is not a pleasant place to be.