I've never really "bought" the whole concept of a "gateway drug."
It's always seemed to me that there's something that you're born with that gives you a predilication to substance abuse, or some other type of addictive behavior. Either you have it or you don't I believe that's one of the reasons that we tend to see alcoholism run in families.
Of course, it's not the only reason, and I know that there are other than hereditary reasons for substance abuse, or addictive behavior in general.
I suppose that I'm very lucky in not being predisposed to addictive behavior, although I was told that my grandfather (a dentist) did become addicted to opiates. But I didn't find it particularly difficult to stop smoking when I decided to, for a while, I thought I might have a drinking problem (while college aged, I spent every night over a summer drunk), so I stopped drinking for about 10 years, and now I enjoy a beer now and then, when I feel like it (about one every other month). I enjoy gambling every now and then, but even though there are gambing boats in the KC area, I've only gone to gamble 3 times. And while I enjoy vacations in Las Vegas, the last time I was there, I stayed for 3 days, but gambled for less than 2 hours total.
I honestly believe that for the most part, heroin users "graduated" from other drugs (cigarettes, pot, coke), simply because the other drugs are far more easily obtained.
Mark