Well, there's the obvious answer: this forum exists because people participate in it. If people didn't participate in it, it would cease to exist. If I value its continued existence (either for its own sake, or for the sake of greater rationality in the world, or for the sake of greater fundraising opportunities, or for whatever reason), then a credible threat of non-participation by a significant fraction of active users threatens something I value, and I might therefore be motivated to change my behavior due to such a threat. One way to make such threats more credible is by demonstrating that users will in fact stop participating over behaviors in a specific class.

In addition to what TheOtherDave said, forums are cheap, and we could just as well be on a site without a dictator if we felt like it.