Yeah, that’s the thought. That or ecstacy or something.
In reality, it’s mostly that it’s so common that everyone who might do “hard drugs” would have been exposed to pot as just background noise, like alcohol or chocolate ice cream.

It only gets a shade of credence because there have been studies indicating that some people start with pill based drugs and then just leave it at that with a “hard drug” incidence rate lower than someone who smoked pot.
The sample sizes are so small that the only real conclusion someone can draw is that it’s not definitely false and it needs more study. But it’s not that important, so funding is slow and unlikely.