Not all mental illnesses are sociopathy/psychopathy. Most of them do not inhibit emotions, and so remorse is still present.
Heck, in my case, I actually have heightened emotions. One time in high school, I felt so bad about saying something to a friend that had a small possibility of coming off as insulting, that I just about skipped 10 - 15 minutes of class waiting for him to come out from whatever he was doing so I could apologize and explain. (I won't tell the story here; just know that the comment was completely harmless and unoffensive.)
Heck, remorse could easily be part of the reason for some outbursts of anger to women (in particular) on the internet. Most men, from what I've seen, want an egalitarian culture as much as anyone else, and at least don't want any sexist views. So when something they take for granted (such as, for example, the damsel in distress trope in video games) is shown as sexist, they get defensive because not only do they not want to be seen as sexist, they don't want to be sexist. Self-criticism is a very rare trait found in people in general, because we all want to believe that we are in the RIGHT! Speaking from experience when I was younger, simply being wrong is, for many people, a terrifying concept, with the fear being more subtly potent the longer the view is held without being questioned externally. Even now, I do feel some fear that I'm wrong, and from being wrong, a stupid, unintelligent (and thus backwards) person.
Such a thing certainly can't account for all, or even most, of the abuse women get on the internet (not just feminists; any woman). But I do suspect that it's common enough to be at least subtly influencing on peers.