Easy. You chose to smoke. You were born with your genes.
Its not a difficult distinction that someone who decides to buy an expensive car has to pay higher premiums than someone who buys a cheap beater. On the other hand, a black man can't be charged more than a white man for the same car. Genes don't seem to make sense there, do they?
Its perfectly analogous that someone who chooses to smoke should either forfeit their insurance for smoking-related illnesses or pay an extra premium to cover them for it.