This might be an unpopular opinion for those who view more rules as the answer.
Banning (or discontinuing or deplatforming or whatever you want to call it) may do little but harden the resolve of key ideologues of whatever stripe. For them, it leads credence to the idea that there is conspiracy against the group afoot. Besides, when has banning actually been effective? Sure, it may reduce manifestation and reduce recruitment, but drugs and spam pretty much show wack-a-mole is not really an effective policy. That's to say nothing of the moral hazards of thought police determining who can say what.
However it is obvious that leaving these kind of groups to echo chamber louder and more extreme, egging each other on also leads to bad outcomes.
Perhaps a solution may be proactive counter speech. Some sort of volunteer regiment or something that finds where these sorts congregate and offers counterpoints to violent idiocy. Obviously flat out threats or calls to action are crimes in and of themselves and should be treated as such.
This would be a pretty thankless task because who wants to deal with this type of idiocy and darkness all day? But I think it could be more effective if properly done than banning as far as changing minds and hearts, especially before people get sucked too far down echo chambers and start seeing the world in a way it really isn't. Other people, smart people, articulate people, right there calling out wrongness, calling out stupidity, calling out misunderstanding, giving counterpoints, arguing for right action, this might be a more effective way to damp down the extremism.