Earlier quoted context omitted.
"Isn't the counterargument to this to point out the Oxycontin abuse epidemic?" No because that's not even an argument.
In fact, it is, because if the pathway to addiction starts with overprescription, deregulation is unlikely to alter the stats: prohibition and black markets aren't gating factors.
Now, if "deregulation" as used above means "stocking next to aspirin at CVS", then sure. But that's not what's being discussed. Haven't done a study of it, but I'm pretty sure Denmark doesn't have many folks heading signing up as addicts to experiment.