It's interesting: if you do a Google search on "is pot a gateway drug," you get split responses on the matter from reputable sources. I know plenty of tokers who never have dabbled in heroin or other hard drugs. Hell, we all probably have friends who smoke the shit regularly and don't do hard stuff. And we all have friends (but it's the vast minority) who started with dope and graduated to needles. A lot depends on the person, IMHO. I never had any desire to do drugs, and didn't. Of course, I used to hunt with guy who was DEA and he and my father made it clear they'd beat my ass if I ever did anything. That still sticks with me to this day.
On the other hand, I have seen the damage alcohol has done to some of my friends and family and it's perfectly legal.