The fact that this is even a question, makes today's society that much more sickening to me.
It has always been known as a nice gesture, and I don't know how it could possibly be considered sexist. The world is falling apart to the point were manners have become sexist or wrong. Gender shouldn't have to play apart in it either. Whether your a man or a woman holding a door for someone, it has been and always will be polite.