Marijuana doesnt "ease them into it". It creates a curiosity factor when they get bored with it. Especially people who do it habitually and develop tolerance to it.
They start with marijuana, like the highs, then suddenly everyone wants to do shrooms, then ecstasy and acid, then God knows what else....then it starts into cocaine/dope territory.
That seemed to be the normal hierarchy when I was in HS...which as many of you know, wasn't that long ago.
People just don't go out and take hard drugs, their is a big intimidation factor when it comes to that....marijuana eases a lot of people's minds about drug use and contributes to people starting heavier drugs a lot more than people want to think.
Actually, shrooms are pretty much like marijuana (when it comes to death/health problems and such), except the difference in trips.
I also don't believe that marijuana causes people to do harder drugs, rather the people around them. I know plenty of people who have tried drugs just because their friends do them. Another good example is when, say a teen, who does marijuana, encounters with a dealer who encourages him to do something harder. "Hey, try some ecstasy, it's better then weed" or something along those lines. Which actually would be avoided with the legality of marijuana, because weed would only be available in coffee shops/dispanseries.