Sadly common, sysop vandalism is the wilful destruction of useful pages by people unwisely granted sysop powers as they attempt to persecute trolls. SV should be distinguished from the relatively harmless wiki graffiti practiced by ordinary "vandals". The extremely questionable use of the community metaphor, as always, justifies the abuse of powers by "authority" to discourage dissent.
Some (trolls of course) consider SV a disorder fit for inclusion in the DSM-V.
However, it has many willing (if normally unaware) advocates who put community over content and thus enable a clique to exclude others and their new troll point of view.