I've moderated a number of forums in my time. And the hardest users to deal with are the ones that insist on breaking the rules 10% of the time, and who refuse to stop. Even if they contribute positively much of the rest of the time, they create far too much work.
(Also, I have zero interest in participating in unmoderated forums. Unmoderated forums are either overrun by spam, or by users who somehow manage to spend 50 hours a week flaming people. Look at any small-town online newspaper where the same 5 people bicker endlessly after every single news story. And if I don't like how a forum is moderated, I find another one.)
There is _always_ a technical solution here. If you can't figure it out, keep thinking. There's never a reason to ban/moderate your core users for 10% rule violations. Instead, that shows a weakness of the software. More transparency helps.