One of the key uncomfortable events of the Harry Potter series comes about thanks to a love potion, and Potter fan Raph addresses the very serious moral and criminal aspects of love potion use with this PSA from the Ministry of Magic. Hopefully, this is covered early on in Hogwarts' health classes.
I dunno, it seems like you have to let your concept of "free will" do all the heavy lifting, here. Genuine love is no less a chemical phenomenon than any "love potion" might be, we know it comes about as a result of chemical releases in the brain you can't really control (indeed, that love is a non-volitional experience is pretty central to our conception of it), but for whatever reason we don't consider sexual consent under those circumstances to be invalid. If you consented to intercourse under the effects of a love potion, I can't see how that's any different than consenting to intercourse under the effects of just regular ol' love, both being chemical influences outside your control. Regret of the act and the sense that one was not "in one's right mind" might very well follow both, but I can't see the difference that makes one of those acts immoral. But then, I don't believe in the existence of free will.