Abuse of specific people on wiki, not of "the wiki" or "the community". Now, obviously we don't mean physical abuse, so
There are no ways to discourage WikiAbuse?, not any way to prevent it, without either becoming an abuser, or changing the way Wiki works (adding security etc..).
On the other hand, vigilant WikiGnomes summarily delete or defang abuse more often than you might think.
Currently, that's "never". I submit the hypothesis that gnomes only "defang" abuse that has no fangs. Abuse made by casual abusers who ultimately simply don't care about the issue or the target. It's a far different thing when the abuser is persistent in their persecution.
[They may clean up months or years later, if a war is too hot to clean up short term, so future generations will be less discomfited. I think that's small comfort, but it doesn't contradict the guy's point above, exactly.]