Theory of Trolls
His theory is that they're actually artificially intelligent programs that were intially conceived by the NSA to annoy the Russians. When relations started to thaw between the Americans and the Russians, these "beings", to prevent their own demise, had no choice but to escape into the 'Net. At first, they lived in Usenet world, but when that environment dried up, they migrated to popular blogs. The jury is out on whether or not they possess capacity for self-awareness. But one must admit that it's a brilliant feat of programming that these creatures can hold two (or more!) logically inconsistent viewpoints at once.
I was amazed that they exist in so many types of forums (forae?), including those discussing relatively mundane topics. I think that's really great evidence for Bill's theory.