DPS display could easily be solved with a system already in game.

[Callinon]

I would expect that very few players who weren't previously trolls would suddenly become such when handed a parser, while players inclined to be helpful and to seek help would have a powerful tool for improving their experience.

Absolutely correct. A troll doesn't need a tool to be a troll. They'll find a way with whatever they have.

Given that, I'd rather have the tools to improve my own gameplay and that of my group/raid. Just because someone will inevitably use it to be a jerk, doesn't mean it isn't a useful tool.