Asking, "do you mind?" is not an assumption of consent. It's the same question, do you consent? It's like asking someone if they mind smoking. It has two implications. First, you can say you do mind. Second, I obviously have a reason I'm hoping you don't.

If you can't say, "I do not like smoking, thanks", then you don't really get to complain, "What nerve! To smoke in front of me!"