You can't make an unmoderated forum as a clearnet site due to legal issues. And even if you set up SMF as a Tor hidden service and promised never to do a single moderation action, soon your forum would be 99.9% spam, and all of the real users would leave. Eventually, every centralized site comes to a policy of at best "everything is allowed but spam and illegal stuff". And this is in fact not too far what bitcointalk.org does, though I guess you think that our definition of "spam" is too broad.
If you want a decentralized forum (with all of the spam and other headaches that entails), it's existed for years on
Freenet.
This.
I'm always satisfied by the way theymos replies to even stupid queries like this one with all the logic and proper reasoning.
@OP : Sometimes when you are browsing the forum and you come across a thread of your interest which you're very knowledgable about and you'd see some replies which are so off-topic and makes you believe that the commenter doesn't have any clue of what they're talking about, the first thing you'd want to do is make sure that post is deleted as it's an obvious case of spam. This is where moderation does wonder.