However, sometimes it does go too far. For example, a few of these accounts have recently been making false accusations of operating a botnet (a criminal act).
I'd argue such false accusations of criminal activity justifies a ban, and other multiple accounts under common control that continue to post would be evading such a ban.
Yeah, plus now they're throwing around claims of actual racism in addition to the botnets. they're literally onto personal attacks of character now, there's not much more you can do with FUD from there. The next step is actual attacks, or a massively broad campaign .. there seems to have already been one escalation, and it would be miserable to see it be elevated further.
I'd agree with banning, specifically temporary IP banning would be a large step in the right direction. Consider the amount of work that would be involved if this forum were to be subpoena'd regularly because these criminal acts were allowed to continue?