I think you'd be surprised how many older staunch conservatives nevertheless experimented with drugs at some point earlier in their lives. And if not drugs, something else that is illegal and carries stiff penalties. The point is the hypocrisy of demanding such stiff penalties for classes of crimes that most people are guilty of at least one at some point in their lives.
If you're poor and black, it's a crime a and should be sternly punished, if you're rich and white, it's youthful experimentation and should be glossed over.