Ask him something about why, since marijuana has been proven to be one of the least toxic drugs (and a natural one at that), is it still in the same drug classification as those which are dangerous and lethal. Then ask him why alcohol which is responsible for thousands of deaths a year is legal, but not marijuana. I am guessing he won't be able to give you a good answer to these questions, especially the last one, so after you listen to his bullshit about it being harmful for developing minds ask him what he thinks the best way to get drugs out of the hands of criminals is. He will be stumped. Thats because the only logical answer is to legalize them.