If something which is also a contraceptive is used to treat some other disease then why not have it treated just like any other cure for a disease? Why not indeed? 

Do note that even the Catholic Church notes this logical difference. Doctrine insists that abortion is an evil that must not happen. Yet saving a life which has the byproduct of abortion isn't a moral problem at all. The Catholic Church is just fine with ectopic pregnancies being treated - the treatment being, in part at least, abortion.