Troll vandalism
Attitudes to troll vandalism (group vandalism by trolls to counter sysop vandalism or to advance a POV that they believe is underrepresented by some systemic bias in neutral point of view) vary as much as attitudes to w:terrorism or w:insurgent activities.
One major question is whether sysop vandalism is actually troll vandalism - whether sysops are trolls or (as claimed in New Troll point of view) the sysops' use of technological escalation makes them deserve what they get and denies them the protections that trolls deserve.
The Sysop Vandal point of view is that troll vandalism is just group vandalism and (of course) that sysops cannot be vandals simply for opposing it even with technological escalation. See Recyclopedia andSOLLOG for typically controversial cases where this is at issue.