Yes but what's the risk?
How often are people coming to work impaired? This alcohol/drug testing process isn't cheap. Millions of dollars are being spent just establishing the processes then millions more to keep it running.
The risk and subsequent testing regime on the roads is 'known'; well sort of. IMHO in the case of roads, you only keep the honest, honest for fear of getting caught.
One too many sherbets, oh I'll be all right, "what if I get caught" is the thought process, not "I could cause an accident".
Those who don't care or don't think about it still offend, hence the multiple offender stats; either significant problem which they can't address or simply not thinking of the consequences.
Surely, by now in this modern world we have processes in place to weed (pardon the pun) out offenders (in aviation) without needing to subject the 99%+ of people that wouldn't offend anyway to such a rubbish process. Hence the fear of 'false positives' and the commentary.
Do we worry about the consequence of false positives with the booze bus? Well no, cause it's not career ending; although it could be if there is a conviction.
My greater concern is the "real positives" that will be encountered by people taking cross counter medications, combinations that my be "real positives", but in no way impair judgement / fatigue / alertness / ability to perform. ie an absolutely honest mistake.
What if a "real positive" comes from medication prescribed by a DAME; used in the correct amounts according to the handbook?
Where is the education process? The "cross" medical examiner saying "cold and flu tablets + flying = could end your career" etc. The easily available list of banned drugs and how many hours between consumption and flying / controlling / tooling is ok?
What change in sick-leave will be attributed to the testing, to those otherwise fit for duty, being cautious because they tied one on 3 days earlier?
I believe that the FAA had random testing and after wasting huge amounts of money it's now targeted "tip off" testing only (allegedly).