I agree with most of what you say here. The trolls don't seem to believe anyone should curtail their "right" to say whatever crap they want. Even when they're on a forum provided by someone else. They have some weird self-centred notion of what's acceptable, and what their rights should be.
Although there's a weird subset of whiners who when you use the ban-hammer on them seem to sort of blame you as a moderator for failling to stop them from going too far. Why didn't you intervene sooner? Why didn't you stop him from winding me up? We had one user who wanted us to re-code our forums to have a special time based banning system, to stop him posting after about 10pm on Fridays and Saturdays. That's when he came back from the pub, in a bit of a confrontational mood...
Others just think you're out to get them. To which my honest answer would be, yup - you're ruining my online community - I'd perma-ban you if I was allowed to. But the site-owners are too fluffy for that. I won't treat you any more harshly than anyone else, but I will enjoy it when I ban you - whereas normally I don't.
Then again, forum culture does matter. El Reg can be a bit rowdy, but it's a pretty nice community. You don't see much nastiness. Although it can get that way, but most of the trolling is anti-company.
I used to mod on an international game's forum. We had our share of arseholes on the English forum, but it rarely became nasty - even when the Mods weren't around. And there didn't seem to be much in the way of grudges being bourne. Except a couple of troublesome users.
Whereas the Scottish forums were an absolute vipers nest. There were a few camps that seemed to have formed, and they'd all participate in bullying certain users. Sometimes it would be all nice, then an argument/discussion would go too far, and then it would just become poisonous. You'd often find yourself having to ban 4 or 5 people at once. And want to ban more, who were egging it on, rather than calming it down or staying out of it.
The Irish forum was different again. Quite rough-and-tumble, but almost always taken in good part. The only problem was we were supposed to crack down on swearing, as the game owners wanted the forums 'family friendly'. We could not stop the users swearing, and it got really silly when we were told we couldn't allow "feck". No power, no God, no force of arms can apparently stop an Irishman from exercising his right to say "feck"...
So I definitely think that user-tolerance is a big issue. Each forum develops its own culture. I've intervened and stopped unpleasantness on forums before, when not being a mod. And it often only takes one person to get the digital lynch-mob organised. The thing about fear of online bullies is that although they're anonymous (for a given level of effort), so is everyone else. There was a brief period on El Reg when someone started down-voting every post I made. Or at least going through my post-history and down-voting every post on a page. Don't know what I did to cause that. But it wasn't terribly effective as an intimidation tool, it's not even that easy to notice. And I guess they couldn't be more direct, as this site is well modded.