This is a good point.
If I go to the liquor store, I can buy bottles that are 90% alcohol or bottles as low as 3% alcohol.
If we legalize "hard" drugs like opiates, meth, etc. then we'll get a similar differentiation along with the benefit that the drugs will be checked by Trusted Sources (both government and industry) to effectively eliminate certain adulterants.
And for the folks who become addicts (physically or psychologically), there's no legal risk in telling their doctor or therapist or anyone, and they can better enter treatment.
There are folks who drink 750ml (~24oz) of 40% liquor every day. It's rare but they have an addiction. They can also get treatment, while the rest of us enjoy 5% beers and 13% wines more moderately.