Part of having the sort of system they are talking about is having choice of drugs, some for recreational use. We can restrict the hardest to do safely (or that have a higher rate of addiction) and restrict frequency of others (we were already doing this with Sudafed in some states in the US a decade ago)- but you aren't getting addicted to opium after one night. You can take pills daily for a week or two without being addicted. Heck, we know that servicemen got addicted to heroin for years during the Vietnam war, only to come back home and go back to a normal life without addiction.
Opiates in general would need a legal way to get high off of them for the rest of the system to work, and we just don't have that and we don't have readily available, science-and-medicine based help for those that do get addicted nor a safety net to ease people's suffering to try to make sure they don't wind up in a similar place.
Part of the reason you make it more accessible is knowing how people use it, and to try to get people to do the less harmful thing in a class of things. So, you know, try to steer people to cocaine and way from meth while recognizing that cocaine isn't alcohol or weed or caffeine.
On the other hand, you probably want anything involving needles to be administered by a nurse. Opiate pills after surgery? Prescription so you'll have enough.
If getting low to moderate level drugs made more sense, why bother with the real hard stuff?
Someone wanting a couple vicodin might be happy to have that option, perhaps with the occasional oxy, and never approach Fentnyl, heroin.
Think of it like a sort of diversion. We know people will do it, and they have human reasons for it too. Copping a buzz isn't any real crime, and people know that.
The way it is now is misaligned with those basic realities. People are at odds with the whole thing, incentives are wrong, risks too high, costs too high, it's just a mess.
So, we enable them to do it and build in friction where there should be some to keep the masses in a reasonable zone where they can just be humans doing things humans do.
I forget the exact number of levels and where all the specific drugs landed but there would a level where you get a physical and prescription for a certain class and it requires regular check ins.
The final level would be for the hardest most addicting drugs where you could only use them in certain places under supervision of a nurse.
There would still be the people who get drugs illegally that are willing to go out side the system (same as there are kids willing to pay a premium to a homeless guy for beer) but it would destroy or greatly reduce the market for illegal drugs