the evil ones are hard sometimes because you feel bad but a well written evil character will have a perspective in which he's admirable or redeemable. Especially one that you play. They have their own internal morality which is different from most people but it still makes sense and they hold to it more closely then the "good guys" hold to their own.
And that doesn't matter
because I don't play evil toons. I tried once, I just can't do it. I don't enjoy going around and doing evil, even in game (in fact, I tend to end up doing good anyway). Albeit, my definition of good and evil is "looser" than most peoples, but even a neutral character would be beyond my ability to do -- I'm too much a natural do-gooder, breaking laws when I feel it necessary but always doing whatever is
right.