If addicts can go to a boring clinic and get it daily for free maybe they'll at some point look up and wonder why they're doing what they're doing.
Especially if the clinic has easily available assistance and things that can help people quit.
Even in the worst case where they remain addicts, at least they won't OD and they're not funding organized crime.
Probably not as easy with meth though - it's one thing to be addicted and still responsive to incentives, psychosis is a harder problem to handle.
Source?
I doubt you’ll find a source, but the number of users distributing small amounts is probably larger than the amount of people pushing weight (who usually don’t use)
This is based of my experience buying heroin in a mid-sized US metro area, fortunately far in my past. One without an open-air drug market, so deals were done in cars or alleys.
If you give out free product, you not only kill the primary demand, but most dealers themselves don't have a reason to continue taking risks - because they can benefit from the free product too.
Purely profit oriented dealers will remain in the market, which is now much smaller and even riskier, since they can only sell to recreational users.