The problem is that you have to take a piss test in order to work in the first place.
I did it once, roughly 15 years ago and never again.

Right now, the terms of one of my clearances states that they can do a drug test any time they have reason to be suspicious (not probably cause, just whenever they feel like it). I signed the paper that said they could, but the terms were if they ask for it, I'll give up my clearance before I'll give up my piss.

While the issue with a clearance is how easily a person can be 'leveraged' rather than just simply micromanaging the citizenry's private lives - I think the general case of piss tests have gone so far overboard that I've taken the opposite approach and deny them unilaterally because I can.

And for those about to argue for piss tests for 'safety' reasons - ignoring all the white-collar workers where there is no immediate threat to safety - anyone serious about safety would do competency testing, the modern equivalent of touch your nose and walk a straight line because there are plenty of reasons a person can be unsafe but still drug-free. And I think this is inline with the original chain-mail, those on welfare certainly aren't safety risks any more than a housewife is.