Corral all undesirables into one ghetto, then destroy the ghetto. The undesirable community runs to multiple other ghettos becoming fragmented in the process. Continue destroying these ghettos and watch as the communities you want to silence become increasingly fragmented until they're no longer able to exchange information. It happened when reddit purged a ton of subs back in 2015. It happened at Voat. It's happened at several chans.