Why do we have drug laws?
Really? If you dont know the answer then it is not even worth debating with you until you educate yourself.
So if some dolt decides to use some substance that he/she has been warned is harmful, well, they can be held responsible to get off of it to make their prospects better, and not have standing given the fact that they were warned about how harmful it is. With measles, given the lack of malnutrition in America, it is overwhelmingly not lethal like it is to starving people in Africa and SE Asia. Having hundreds infected in a nation of 300 million is far from a true national outbreak.