For me, it dependds on how the scene is played out. I read a German fic where Harry was captured by death eaters, and Draco was a spy for Dumbledore. They allowed Harry to choose who would rape him, and he chose Draco. It was told in Draco's point of view, and he'd been secretly in love with Harry since they first met. That one sorta turned me on... it was both erotic and horifying because of Draco's mixed emotions about what he was doing...

As for rape being about power, I believe that's usually a case. But I think sometimes it can also happen that someone is so obsessed with another person, that if they can't have their consent, they'll eventually use force. That's why people who believe in love potions always warn against them, because if you change your mind, that person might not be able to stop themselves. Makes for an interesting fic, wouldn't you say?