Don't you think most people who would be interested in buying heroin in the store can already get it?
There's also an implied suitability in the sense that "stores wouldn't be allowed to sell if it was really that harmful". This may or may not be true but it certainly impacts our cultural mindset around alcohol.
https://www.google.com/search?q=chart+marijuana+usage+in+col...
A lot of people got (get) "incidentally" addicted, due to overprescription / easy supply.
Regulatory failure and corruption didn't help, of course.