It's an excellent question, I don't think its possible to predict the outcome. In places where heroin is both easily available (low friction) and there is little social stigma attached to it, you get folks wasting away in opium dens, but not everyone who could be in those dens, are.

No doubt a lot will depend on how functional folks can be while 'high'. I have known people who were essentially 'pill heads' or addicted to oxycodone such that they were constantly under the influence but they were still able to do the job assigned to them. (I make no judgement as to whether their performance was improved or hampered by their drug use). Perhaps folks could dial it up or dial it down depending on their need.

But what scares policy maker types is that you have an unpredictable effect if something comes into existence. They will try hard to prevent its creation because of the possibility of bad outcomes even in the presence of the possibility of good outcomes (perhaps you'd have lower workplace rage events if people could dial in a mild soporific state).