I agree with you. The residual remains in the body for awhile, but that does not mean the user is incapable of performing the job during the week, usually. Of course, many exceptions are inferred here, and I agree the employer has the right to handle pot smokers/smoking in any way they want and too dam bad for the employee/prospective employee. What has not been mentioned is second-hand smoke on the non-smoker, but who is tested and terminated or punished in some way. So then thresholds are applied, similar to DUI’s, etc. Over the limit, punished; not over the limit, warning, and other procedures.
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.