Dalswyn: Disclaimer: about twelve years ago, I was a moderator on a forum with thousands of regulars. I had to deal with abusive members, with trolls, with alts, even with far right propaganda. They -all- lost patience before I did. They -all- scampered off. Did some people complain about how tough we were? Yes, some people complained (and yes, we were tough). Did it kill that forum? No. It's still thriving, it still has active members in the thousands.
jamotide: Right...tough aka abusive. And thousands of boring members no doubt. No thanks.
I don't think there's any equation determining that, be it one way or the other.
Have you been browsing the Penny Arcade forums, for instance ? It's pretty heavily moderated, and quite often an amusing read.
You have cool moderated and unmoderated forums. And awful ones too. Other parameters determine the outcome (the kind of people in the forum, the kind of people behind the forum, the kind of rules that are expected to be followed, the degree of "spirit" or "letter" in the interpretation of these rules, etc).