You're not a law enforcement organization. You don't have the ability to investigate and determine whether or not the threat is genuine or if it's an agent provocateur.
Banning them creates a hazard, since now to get an opponent banned from the service, they can create content that reaches to this level.
What I don't get is how online forums with free registration have been a thing for WELL over 30 years now, yet some people think that the possibility that people make accounts to deliberately post things to get the forum sanctioned is still viewed as some insane conspiracy theory - and you a monster, if you suggest the good guys would ever do such a thing "to themselves".
Banning them creates a hazard, since now to get an opponent banned from the service, they can create content that reaches to this level.
It's a Layer 8 DDOS.