A few beers does most people no harm. A few hits off a bong won't kill most people - maybe any people.
But what about the chicks that get “loose” after a hit, or when they get drunk? They will often trade sex for drugs, while guys trade drugs for sex. From my observations a long time ago, it doesn't take long to get really basic in human psychology.
The other issue I see is mixing drugs. Been going on long before fentanyl hit the streets. A night of pot use combined with drinking leads to very different outcomes than a night with a single home grown (quality controlled) joint.
When I was young PCP was the drug of choice to mix into pot, to get a stronger high. And the pot was not nearly as strong as today's stuff. Dealers mix in a stronger drug to get increased sales, or to achieve a more nefarious outcome.
Predicting the effects of pot use seems to have many more variables than predicting the effects of alcohol use. We simply do not know enough to effectively police its use.
Both alcohol and drugs have been used and misused in my family, as in virtually everyone reading this. Neither had many positive outcomes from what I could see.
The problem I see if removing a stigma from something that clearly alters our brains...especially the brains of young children. Remove the stigma and make it more available and INVARIABLY it will increase. Look at abortion..prime example.