As seen in recent events, preventing new members from creating threads can cause just as much annoyance as freedom in posting. I've always thought the restriction caused more trouble than it tried to prevent and, additionally, stifles forum growth. If someone comes to a Mario forum with something interesting to share about Mario, why should they be forced to jump through hoops to do it? They're either going to A) disrupt unrelated threads to ask/complain about it or B) just not bother to share with us.
Yes, there's a good chance it might be something dumb they want to create a thread about but it's sure easier to avoid a specific thread than avoid some new person posting about something you don't want to read in threads that you do. If you see a dumb thread, just let it die. The only problem arises when you enter their thread specifically to complain. So if you can resist that, n00bs being able to post threads is clearly the best option.
Be a Creationist. It will clean up existing threads, encourage forum growth, and at the least, give us more to talk about.
Plus, they can be really funny!