not really, but imagine that you're a drinker that also smokes pot occasionally. what do you do when alcohol no longer gives you any satisfaction? increase the consumption of the other, or if you're not using smth else, look for other stimulants or disinhibitors. it's not about gateway drugs, it's about addiction swapping!

Edit: + and it's not like if you're a pot smoker, you're gonna start doing heroin when pot is no longer enough for you, so I don't believe in gateway drugs.