This might be a really stupid idea, but going with Crystals idea, on top of that, maybe make a rant forum at the bottom of the main index, with archives, which still, would have rules that the rest of the place has, to respect, etc. But if people are going to rant about how much they hate the place now, or whatever stupid reasons they are leaving for, or general garbage that nobody likes poluting the rest of the forum, they can just do it in the dump area of the forum for loser posts. Because meerly making that change will only cause them to move into community speak to tell their story. And hopefully, this way they would just go to "the dump" or whatever to say it. Staff would still monitor it for flaming and what have you, but this way it is not flooding the introduction area, or causing chaos in community speak. "IF it catches on" Plus nobody will complain about these kinds of posts anymore because they are in their own garbage area not disturbing the rest of the forum.
I never fully thought through this yet, It just popped into my head when I read Crystal's post, so maybe its not a good idea, but I thought I would mention it anyways.