Ask any professional in the field and they will assure you that rape is primarily about violence, not sex. It's the only weapon a man can carry with him absolutely everywhere without being identified as a potential attacker.
You're thinking like a normal, reasonably healthy and well-adjusted man. The only reason you would force yourself on a woman is that you find her attractive and (at least somewhere along the way) thought she was interested, and you're both plastered. But normal, reasonably healthy and well-adjusted men are a small minority of rapists. The vast majority of rapists have a couple of screws loose, often from some untreated psychological problems from their childhood. Quite often they were abused by their fathers, and not necessarily sexually.
Only in "date rape" do we find testosterone-crazed young men who are otherwise fairly sane and healthy believing the old crap about "no means yes," and with their abominably poor communication skills misreading clues, while both they and the equally young and inexperienced women have had too much to drink and are unable to express themselves clearly.
I can believe in the rehabilitation of a date-rapist, who at least has tried in his clumsy way to form a relationship and in his alcoholic stupor is sure that the lady will enjoy it. But the more typical sleazebag who picks on strangers and starts off with violence rather than foreplay? No. He's just wired wrong.
Castrating rapists doesn't work. They just start assaulting women with broomsticks and other objects. This alone is all the evidence we need to realize that it's primarily about violence. Men know that rape is the one kind of assault that many (probably most) women never completely recover from. That's what they want: permanent injury.