"My guess is that criminal laws against marijuana use have become culturally untenable. At this point, if you want to maintain criminal laws against more dangerous drugs, you're better off conceding the legality of marijuana, lest the public lose respect for drug laws in general."
This is an extremely important point that people frequently miss. When children are told that little white lie, that all drugs are dangerous, they will find out the truth someday. Then they will wonder whether the whole thing is a lie. You can almost see the thought process:
"I was told that marijuana was dangerous. I tried it, and now I know it isn't very harmful. I wonder if the same applies to cocaine and heroin?"
Also, I know quite a few people who smoke marijuana on a regular basis. I could make a phone call and get marijuana in about 30 minutes if I wanted. Here is the kicker. If I wanted some cocaine or heroin, I could get it in about an hour. How? Because I'd call the person who could get me marijuana, and they could call their dealer who could almost certainly find them other drugs. In other words, marijuana is a gateway drug precisely because it is illegal. If I was given a challenge to find cocaine or heroin, with the stipulation that I couldn't use a pot-smoking intermediary, I wouldn't know where to begin.