Still, hypocrisy must surely be the least of a demon's flaws. Maybe that's all there is to his interest: a drive to gain new knowledge, specifically of what it's like to kiss a human. This drive is probably the one motivator in the entire universe Hermione truly understands, since it's more or less the same reason why she even gets up in the mornings. She can hardly deny someone else their own attempt at acquiring a new experience.