It's not inconsistent to treat different things differently and different drugs are
radically different in their individual health and societal effects.
I live in Seattle where marijuana is legal. Alcohol and marijuana are widely consumed and I rarely see any large-scale problems from it. Obviously, there are many people who can't handle either of those, but their failure to handle it well seems to not impinge on others as much. And, compared to them, there are a huge number of people able to consume alcohol and marijuana in a safe, healthy, non-problematic way.
I also live next to a couple of homeless encampments. Many of the people living there are clearly addicted to opioids and/or meth. In just this month and within a mile of my house:
* I saw a woman, topless, brandishing an umbrella, wandering between the sidewalk and into the street screaming at no one.
* A man was shot in the stomach in front of a food bank.
* Another man was shot in the neck at an encampment.
* A drive-by shot up an RV and car. (The people inside fortunately weren't hit.)
There's more I'm sure but these are just the ones I know about in the last few weeks.
It's entirely consistent to say that we should treat drugs that lead to the latter behavior differently from drugs that don't. Opioids and meth are incredibly destructive. I'm not saying what specific policies I advocate for them, just that it is reasonable to have different policies for those drugs compared to others.