I think you're going to have inane trash on any message board besides the ones you have to pay for. (and, well, who would pay for a message board.) the alternative is to require registration and to appoint moderators, but I've seen that situation go sour recently on one site that I post regularly on. instead of banning only the inane posters, people who disgreed with site policy and badmouthed it were also banned (of course the site can do what it wants, but the banning of posters who simply badmouthed your site doesn't cultivate an environment conducive to free discussion).
I think that while we should be concious of the threads we contribute to and of what we say, you gotta take the yin with the yang. it's not too hard to read through the noise and find the good stuff on here.