I think that's the recurring lesson of online communities: moderation works. Without it, the community will eventually degenerate into a haven for trolls. Unless it was always meant to be a haven for trolls; then it will become a haven for different trolls.

Maybe this is a sad lesson. I would prefer if a completely unmoderated discussion could remain civil and constructive at all times, but there's probably a reason why even panel discussions with only a handful of people need a good moderator.