Rubbish. According to research cited by the Institute of Medicine, of all those who have ever used heroin 23% of them became dependent, whereas for marijuana the corresponding figure is 9%.
Anyone that thinks that being addicted to pot, that is easy to get, would not lead to heron or crack is kidding themselves.
Recent studies by the RAND Corporation, and by economist Steven Pudney of the University of Leicester, have deflated the "gateway theory."
The major problem with drugs is that the outcome is much worse than liquor. Why do you think they call it DOPE.