As I said, "even if there is a correlation, how do we know it's not the welfare that causes the drug use - or that both being on welfare and using drugs are caused by a third factor such as a poor attitude toward life?"
The important point is that without the drug addiction, many people might be self sufficient and independent. This is common sense.
Certainly, there would still be people looking for a free ride. But it is very hard to deny that drugs can be debilitating to the point where a person can’t or won’t work.