is there any evidence to support the idea that having places for hate speech to grow has a quarantine effect, reducing hate speech elsewhere? Studies on the effects of banning hate speech communities suggest that the mechanics don't work that way. For example, when reddit banned /r/fatpeoplehate and other subreddits centered around hate groups, other subreddits did not inherit the hate speech problem, and former hate group users reduced the amount of hateful content they posted.

http://comp.social.gatech.edu/papers/cscw18-chand-hate.pdf