I had a moment of insight. Even though rape is a sensitive topic to me and most I will talk about it now, purely from a logical perspective.
If you think about it... it's weird, isn't it? Why would someone choose to seek individuals and have sex with them, against their will, when they could just make themselves presentable and find a willing person to do it with..? I guess it could be easier that way. It could be a certain amount of limitation imposed on them by their social conditioning and (lack of) social skills they have been given/picked up on. Could be several other 'reasons'.
At the end of the day, it is a choice they are making. Why would they make this one? At the deepest level I believe it's innate.
When we make this claim we usually look at the 'why would have this been useful'? An explanation that has been put forward is that individuals that are incapable of finding a mating partner use this method of spreading their genes as a second best option.
I think it makes sense if you think about what some enjoy in sex play. We don't have to go as far as violent fantasies; take the victimised ones for example. It seems far too common for people to find a certain thrill in either partner being helpless for it to be a coincidence. Being tied to the bed, role play of one partner being dominant... these all mimic rape, which seems to indicate that there is an innate tendency towards it for some of us.
This seeming tendency, at least to me, looks as though the evolutionist theory of forcefully spreading one's genes is correct.
NB I know this is a sensitive topic to most, please note that this post is purely about the logic of it. I am not stating anything about the morality of the issue.