Let me be very clear, I am not disagreeing with your point. Nor am I agreeing. I’m simply stating that your conclusion does not follow for the form of your argument, and providing an alternative example.
The form of my argument is that it is significant that there are not massive amounts of psychosis historically correlated to cannabis use, like we should have seen if this study is valid, and we really would have noticed. You're suggesting no one noticed alcohol was bad, either, but this is false. In fact, alcohol has been widely recognized as being destructive since it first became popular. That no one did any studies on the effect on fetuses until the 1970's is incidental, as anyone should have been able to guess this correctly without a formal clinical study.
Regardless of alcohol being a poor replacement for cannabis in example or metaphor, it is still a straw man argument.