We are supposed to imitate Christs morals, service, and love for each other. That doesn't mean that we walk everywhere we go, wear sandals, never cut our hair, and lay on our sides when we eat. Those things are unimportant. It's the spirituality that we are striving for. But who's to say that smoking one marijuana joint twice a month while relaxing in the living room is any worse than watching a football game on sunday when we could be in church, or out evangelizing? Or having 6 pairs of new shoes in the closet, when our neighbor has none? Or offering only words of encouragement and advice to a family member who really needs our financial help? Or having our heart filled with hatred for someone who has wronged us? Or being filled with anger when someone cuts us off on the freeway? Christ said, "He who is without sin, be the first to throw a stone".
As I have stated before, I do not believe that a spiritually mature Christian should smoke. However, that is a decision that each individual has to make for themselves. But the drug war in this country is hideous. The cure is much worse than the disease.