Good point. Drug tests actually don't test for a total absence of metabolites, they do test for a certain level, and those exposed to second-hand smoke can have a high enough level to test positive even though they, themselves didn't personally partake.....so you are now into 'freedom of association' territory because of false positives.
Then you have some who DO partake that are intelligent enough to know how to beat the urine teat by creating a false negative, which pretty much nullifies the entire point of 'testing'.
It's just nuts! You can either do your job, or you can't. Whether that 'can't is because you're high, drunk, or just too stupid for words really is a distinction without a difference, IMHO.
“No Smoking” means NO SMOKING
not hard
The business can still make smoking pot against the rules and a firing offense. There are governments that won’t hire smokers, so its okay for a business too