Most BL mangaka are women, right, with a primarily female audience? So if they were to write a story between male and female characters, would they even think to use rape as a starting point of a relationship? I doubt it, even though I've read that the Japanese may view rape a little more leniently than Westerners, because of its alleged ubiquity there. Perhaps the writers believe (Japanese or all?) men use sexual violence as a way of expressing tremendous amounts of attraction for the other person. Indeed, the words "I won't be able to control myself", "I can't hold back any longer", etc, I've seen many many times in hetero and BL manga.