Actually, "free speech" doesn't even necessarily entitle you to scream in the streets. While the 1st Amendment pertains to government actions and citizen speech, it is a settled principle of jurisprudence that the government can regulate time, place, and manner. So, even if this were a government Web site, posters still wouldn't enjoy unbridled freedom to post anything that crossed their minds and exited their fingertips.
Personally, I'm all for open exchanges of opinions, but anyone who has frequented other boards will know that a few loud and active voices can dismantle the whole atmosphere of discussion. That's why I generally like this board. Idiots aren't allowed to ruin it for everyone.