Indeed. The difference with alcohol is that after 24 hours or so, you generally can't detect it because the body works so hard to rid the body of the poison that alcohol is. Pot, on the other hand seems to be fairly well tolerated by the body, and given the levels that can be detected by modern methods, it can be detected a month later, long after it could have any actual effect on someone's ability to work.
Don't care for drugs myself, though I will cop to an occasional beer, though seldom, if ever to I drink more than a couple at a time, and even then it tends to be spread out over multiple hours. Personally, I wouldn't give a damn if someone working for me smoked on the weekends, as long as it's not at active levels when they were at work. Trouble is, with many drugs the answer seems to be a binary solution set. If present, it is verboten, regardless of whether it was last night, last week, or a month ago.
The current answer, of course, for those wishing to be gainfully employed is not to ingest any of the proscribed substances at all. Such a necessity doesn't affect me directly, as I'm unlikely in the extreme to do so in any case, but it seems a bit silly to me.
The really bad part about this is the possibility of false positives. Because of the way these substances are tested for many innocuous things can lead to false positives. Sure, in most circumstances, you can retest, but regardless of the outcome of subsequent tests, there is always that cloud hanging over one's head that they did, in fact, test positive for a proscribed substance. This can have consequences to one's future even through no fault whatsoever of the individual in question.
This is the main reason that I think near universal testing is a bad idea.
The only false positive I’ve heard of - and close to someone who has had to do multiple drug tests for work etc - is eating poppyseed bagels can make a false positive for opiates.
False positives? That’s why there’s always “Sample A” and “Sample B.”