Evidence is that when large social media sites ban hateful groups, they re-congregate somewhere else in much smaller numbers. So while the bans don’t eliminate all of them, they are actually fairly effective at turning the temperature down.
Consider people like Alex Jones. He’s still making stuff, his hardcore fans still subscribe to his stuff, but he’s lost all of his marginal followers as well as the massive on-ramp that YouTube provided him in the form of search and recommendations.
https://www.vice.com/en/article/bjbp9d/do-social-media-bans-...