Oh! I think they are. The sole purpose of any species is to ensure the perpetuation of its kind. Human beings need to be inherently sexual for the survival of the race.

They are just more evolved and have other things to do than just eat, sleep and have sex. This offers some distraction from sex. Otherwise, being sexual beings is in born and they would do it more often were it not for their other life endeavours.

Are breasts inherently sexual? Yes and no. It depends on the context. Just like lips, hands and buttocks can be sexual or not based on the situation at hand.