You're suggesting that trolling is always bad, which you derived from the averaged experience that trolls are bad, therefore it's bad even when good people do it for good ends. It's the same naive argument that all violence is bad, or all censorship is bad, therefore good people should never ever be violent or censor. Just as I'm fine with good people using violence for good ends, or censoring stuff like porn or other degenerate crap, I'm fine with good people trolling actual trolls for good ends.