As others have said, its something that sounds good but at its best ends up being a waste of even more resources. That money would be better spent on positive drug rehabilitation programs, or even just employing more social workers (who by the way, are actually one of the prime ways that they detect drug problems and other issues that drug tests aren't going to catch). Legitimate studies seem to indicate people on welfare programs are actually less likely to be drug users than the normal population (the people saying if they can afford drugs were partially right, just in the opposite direction, if you can't afford food, you probably can't afford drugs much).
Drug testing is quite limited in that unless you basically did the drugs within a quite recent timeframe, the only thing it will really catch is marijuana. Your chances of catching alcohol and harder drugs are pretty slim. There's flaws in drug testing itself, and by that I mean how valid and how reliable it actually is.
There's also the fact that drug addicts are exactly the people who need these programs. Literally that's one of the things they were specifically created to help with. It also would mean denying social benefits for the kids of drug users.
Oh, and don't forget how the pharmaceutical companies created a ton of drug addicts by pushing synthetic opioids that ended up getting people addicted. And there's plenty of people that got hooked on pain meds because of legitimate injuries. You're basically wanting to light these people on fire after kicking them while they're down.
There's that whole 4th Amendment problem that keeps coming up with this type of thing too.
Why stop at drug testing? Why not block benefits if people buy lottery tickets? Cigarettes? Porn? Alcohol? Abortions? Birth Control? Junk food?
Hey, I bet if we dig deep enough we can find a reason to deny benefits to everyone, so the hungry can starve and the sick can rot in the street.
Thanks for posting OP, you fucking piece of shit. I'm glad your children benefitted from a social program you would deny to everyone else's children.
Some states actually were trying to do that, and I think they even wanted their purchases regularly audited.