Several years ago I spent a couple of weeks trolling both of the SPCA's forums. The members and administrators might have been horrified, but they didn't ban me for my comments. The fish in the barrel there were probably mostly 12 year old girls, so there wasn't much entertainment in the end.
DU is a whole nuther level of herd mentality in which the herd practices social eugenics to control association and ideas. A prototype for dictators. Also a good place to start your hunt for Americans that would kill Americans, and although that crowd will mostly depend on hired strongmen to do their dirty work, there will be plenty that would take joy in killing their countrymen with enough encouragement.
They're dangerous, but mostly to ideas, a paper tiger full of limp wrists.