I don't mean Slashdot per se, but quite simply it's the empowerment of the internet that fuels this. When I was a kid, you had very clearly defined vectors of dissemination - newspaper, books, tv...if I had an outlandish opinion about NASA faking the moon landings I would literally have to get a book published. Or better yet, have a Hollywood producer read my book and think "I can make a movie out of this - say, I wonder if Jim Brolin is available?" Bang - instant commonly known conspiracy theory.
Now, who needs Hollywood? I can have a blog, get interviewed online, find plenty of wackos out there trivially to join my cause and spread the bullshit. It's the "democratization of the internet" that's the problem. So we're screwed, unless of course we can educate all these boobs to learn how to think and recognize something dubious when they read it. Hasn't that always been the problem throughout history?