Why is killing, however brutal, acceptable, but rape just plain isn't?

Allow me to set the scene. There's this neat comic called Wanted which just released its second issue. It's written by Mark Millar, drawn by JG Jones, and colored by Paul Mounts. It's an interesting story, about a regular guy who suddenly finds out that his recently deceased father was a super villain, and now he has the ability to become one too.

So we're watching a regular guy, someone who gets bullied by life, become this hard ass (think Assassin's Apprentice by Robin Hobb, only in a modern world, comic book villain way). And the protag is killing people, and beating people up, and I'm enjoying watching this transformation...

Then, in one panel, there's a casual comment about him raping a random big name (unnamed) actress, and how it never makes the news (his illustration of how much the villain organization controls what the world knows about what they do). And then the story goes on.

And while it's still a good story, that one line took something big out of it for me. Somehow all the brutal killings were okay, but rape crossed some mental line, which instantly made what I was reading less than it was before.

The seemingly stupid question of the week is: why?

Sean's suggestion was that they really were different levels of, for lack of a better word, evil. That killing was over when it was over, and that raping someone was more like torture, giving the victim something s/he had to subsequently live with and agonize over.

I've been thinking about it more, and while I think he's right, I think there's something else to it. This was heightened by my response to it as a woman, and with my almost innate agreement with what Sean voiced, but oddly, I think a big part of it may be this: Super-villains, comic book style super villains, don't rape.

It's a stupid statement, isn't it? But they never do. I just don't see Doc Oc in a Japanese tentacle flik (I mean as part of the main story--though I'm sure someone's fan-created version is out there, and no don't send me or post me links). You don't see Magneto or Green Goblin as sexual predators. Somehow, comic book villains are either too ridiculous or too dignified to be out there raping people. Rape seems too undignified, somehow too wrong, to be part of an enjoyable villain.

Now I realize that Wanted, or perhaps more accurately, Millar, is trying to make a more realistic villain here. More of a real world bad guy. And rape is a real world bad thing. The problem for me is that, while lacking the words to adequately explain it, this particular bad thing threw off my identification with the character. Would I have had the same reaction if it had been done in another series, or is it a "comic book" expectation which makes this seem wrong?

It was a minor part of the story, but my reaction raised a lot of questions for me. Thoughts?

I work the next few days and nights, so my return comments may be slow, but please comment. I'd like to know other people's thoughts on this one.