Marijuana as a gateway to what exactly?

I was just wondering why people still believe the fifties propaganda that marijuana is a gateway drug. I could understand it if they meant that people like to experience different sensations but the whole concept of a "marijuana addiction," (which is so much bull to begin with) leading to other addictions seems so strange a concept to me. I have tried many drugs but the only one I found appealing was marijuana so I didn't do the other ones again and I use marijuana in moderation for specific purposes like I do any foreign substance I ingest. Do people not realize that every different drug brings a different kind of effect and addiction to one is completely different from addiction to another?