Free speech or moderated speech?

Should we really keep holding up free speech or free expression as the ideal for public discourse? The reason we try keep speech free is not because there is some ultimate value to the ability to express oneself in whatever way one desires, but rather because we don't want to prevent someone from saying something worthwhile. In practice, we have a number of ways of moderating public discourse: a newspaper doesn't publish just any editorial, after all. We try to direct the most attention to the contributions we think will be most valuable, and we try to shuffle the cranks off to the sidelines. The goal is to let people make genuine contributions to the conversation, not to treat unequal contributions equally. On this view, speech that threatens the core beliefs of the community directly (incitements to violence, enemy propaganda) can be barred, and indirect threats can be gently hushed. Of course, in a pluralist society, we do want to construe acceptable speech as broadly as possible, but we also want coherence. Do you learn more from a symposium in The Atlantic Monthly or a YouTube message board?