There's an important caveat here though ... nobody is forcing you into a line of work that requires drug testing.
I've got a close friend of over 30 yrs that works as a mechanic for an oil company. There's always been sort of a friendly competition with us so if one has a trade skill that the other one doesn't we try to acquire it.
It's fifteen years gone by now but back then i was driving year round. I had a licence that he didn't so he was going to see of he could branch out a little in the company and spend some time running an 18 wheeler loaded with 20,000 gallons of petrol from the fuel depot to the company tank farm.
We were talking about it and at the time he had a bit of a crack habit. I really didn't take it head on but suggested that what somebody does in their off time is really their own business -but- when you've got that commercial licence you're subject to random testing. He understood ....

All these years later he's still working for the same company as a mechanic but he never followed up on driving truck.
It's just one of those situations where you can do one thing, you can do the other thing, but you can't do both. There's good enough reason for it ... there are some high risk jobs where your head has to be completely in the game because you could easily get yourself or someone else killed.
I've seen what happens first hand when you're not at your best on a large construction site. Come noontime some of the guys would go out for lunch and hit the bar in town ... maybe even toke up off site.
After lunch was not good ! You didn't want those guys working anywhere near you and especially not overhead. The quality of their workmanship was off and they were prone to making mistakes like accidentally dropping a hammer while they were working up on the roof.
I quit that condominium project after about a month and a half. The working conditions were miserable and things weren't going very well. I heard that the whole thing went into bankruptcy a few months later.
Sorry .... it's just an old fart telling his stories but i draw from personal experience more than anything else. I've been on both sides of the issue. Back in the day i was pro legalization but i've been away from it for awhile and look at it from a different perspective now.
lol .... thread drift or what ?