It’s a good and clever scheme.

First, the clinic provides good clean needles, so no risk of cross-infection.
Second, with the addicts going to the clinic, that takes money away from the local drug dealers, why pay someone when you can get it for free?
Third, the drugs are clean, not cut with anything that may be dangerous to the addict’s health.
Fourth, they have medical staff on hand to help the patient in the event of an overdose. Most OD’s are survivable, provided they get medical attention in time.
Fifth, they are offered councilling services and recovery programs to help them get clean. You’d be surprised at the number of addicts who are just taking the drugs to not feel the pain of withdrawal, and remain addicts, simply because they have no access to decent programs to help them get clean.

It has been proven to be effective and drug addiction in the Netherlands is at an all-time low. If more countries treated drug addiction as a disease to be treated, rather than a problem to be demonised there could be some real progress made.