Because there's another possibility. The one that describes me in fact: I don't personally use marijuanna, nor do I want my children to, but I believe that choice should be left up to individual adults to make for themselves. Note the carefully chosen words: choice, adults.
I agree, and I also believe that the criminalization of marijuana causes MORE harm than marijuana use itself does, through the growth of organized crime and drug lords, and the incarceration of people who are doing nothing more than using the drug in their homes to no one's detriment but their own.

Mike's own personal loss due to marijuana use is hard for him, but I think it's dwarfed by the consequences of encouraging the illicit drug trade by criminalizing a drug that is no worse than alcohol. We tried that once. It didn't work. It isn't working for marijuana now, either.