There is that, though that's not the point I was trying to make. Yes, people who are willing to break the law for one drug are more likely to be willing to break the law for another drug. Certainly more likely that say, a Glenlivet drinker cruising the streets for a crack cocaine dealer.
Also, there are those who prefer an illegal sub-culture drug instead of a socially acceptable one. Getting high illegally is half the high.
(A side note on that. My friend's wife had been having an affair with this one guy for years. They decided they were in love. She divorced my friend to marry this guy. They never did get married and broke up after 6 months.)
No, my point was that the pot smoker has an addictive personality. He looks to a recreational drug to fulfill some need. That personality would make it more likely for him to move on to another drug.
(Yes, alcoholics also have addictive presonalities but we're not talking about alcohol. The thread is about marijuana.)
That's a blanket statement, though, that's not entirely true. Some people smoke pot on a casual basis, others once or twice, and still others get mired in the whole pot subculture and make their life all about smoking pot. I've known all types.
If that's what the "gateway effect" boils down to (and I think it does), then it's no more basis for banning any one potentially addictive substance than any other.