It's fighting fire with fire. Spammers and malicious attackers often brigade and/or use bots. It's easier for them to overwhelm moderators than to be moderated.

It's fighting fire with fire. Spammers and malicious attackers often brigade and/or use bots. It's easier for them to overwhelm moderators than to be moderated. Shadow and heaven banning are countermeasures. They aren't perfect and can be detected by determined attackers. Yet they raise the bar for abusers.