I'm a former narcotics investigator, and I can tell you, the drug war is a failure. I don't know anyone who reached 21 and decided to start smoking tobacco. I think marijuana should be legal for adults, but we need to keep kids drug, alcohol, and tobacco until they are 21.
We have reduced tobacco use dramatically using education, no one went to jail, no families destroyed. It's sad but today if you want to find drugs, ask a kid, if you want alcohol, you need an adult.
To legalize or decriminalize marijuana, and how to do it will take a lot of talking. Anyone with a legitimate need should have access to marijuana for medical uses.