Quite a few people have doubts about the idea that most rapes are not sexually driven but instead about power. For the time being I'll go with the specialists idea that was formed from years of research amongst scientific peers rather than from a strangers gut feeling.
A post earlier mentioned some women having rape fantasies. All I can say is those were fantasies I'm certain those women would not want to actually be raped. I know it sounds absurd to have a fantasy like that but are more "normal" fantasies much better?
For example: You watch an action movie and think "wow... it sure would be cool to like that hero!" However, the reality of that movie would be you getting shot at by tons of guys with your life in constant danger regardless of what amazing skills or cool gadgets you had. I doubt it would be as fun as your fantasy made it out to be.
All of that said I'm certain its possible some rapists may simply not care that they are causing harm to someone. That doesn't neccessarily mean they are sociopaths they may just not have learned any differently. Supposedly right and wrong are subjective.