in the history of mankind there has never been an "evil" person. all people are essentially the same. some are simply less informed, sane, well adjusted, etc.. than others. even hitler honestly thought what he was doing was right. i seriously doubt there was ever a point during anything he did where he thought, "dude, im one evil sob". he didn't gas jews then bust out in a fit of maniacal laughter.
all these nutjobs spout off how they are doing "the lords work" not because it says in the evil guy handbook that you have to. these people honestly and truly believe that what they are doing is right and is the best thing for everyone. noone ever believes "they" are the bad guy.
in a group people tend to allow their own morals be drowned out and adopt that of the group. germany is a perfect example of this. it wasn't a country full of devil worshipers who hated jews. it was a country full of people who were desolate and desperate for direction. terrorism is cut from the exact same cloth.
the mass majority of people on this planet are weak minded followers desperately searching for someone to tell them what to do.