It turns out that if you ban a certain set of users they will react strongly, often causing many more problems. At Chesspark I was just amazed at the lengths people would go to to get revenge for some perceived wrong when they got reprimanded for violating community standards.

Making them think nothing happened but removing them from the rest of the site is extremely effective.

Blackholing IPs is a poor solution in practice, since many users can change IPs on a whim, and some ISPs run DHCP out of large subnets that may contain respectable users.