I think what makes Magneto a great villain is the fact that he doesn't see himself as one. He's willing to be the seen as a bad guy but only because he believes everyone around him is misled in their opinions of his actions, which he sees as noble and right. Everything he does he sees as necessary. He's not cruel for cruelty's sake, but does it as a means to an end... Accept that one time he imprisoned, tortured and filmed various X-Men being intimate, ultimately as a distraction. Completely personally forgiveable. Friends and lovers do that to each all the time.