I wouldn't say JWs are evil, because evil implies intent to harm. Most JWs indeed do evil things, but they're deluded and controled in such a way that they actually, deep-down, believe that they're being good people.
Everyone wants to paint the world in black and white with evil people and good people. The reality is that we're all just people, a product of our genes and environment. Given the right circumstances, you can get just about anyone to do evil things. It's a scary notion, but I think being in denial of that fact only leads to more evil in the world. If people are allowed to keep this black and white view of good vs evil, it only makes it easier for them to justify evil actions. If people are made aware of just how easily anyone can be made to do evil things, they may be a little more on gaurd to ensure that they don't fall into the pattern of rationalization and groupthink that seems to be the cause of most of the bigger attrocities.