They aren't the worst. They do say some pretty anti-semitic things at times however from what I've seen (some of them think the world is controlled by a Jewish conspiracy or some such).

/r/conspiracy has quite a diverse set of 'characters', the anti-semitic ones are merely one of the loudest. There's also the various 9/11-truthers, the flat earthers, UFOlogers, Christian/spiritual scientists, pro-gun/anti-federal government types, etc. It can be a pretty fun place to check out, actually, if you enter it with the right frame of mind.