It depends on how it's applied.now to make this real interesting: are you who claim drug testing is unfair/irrelevant/other apply the same muster to a security clearance?
A zero tolerance approach is overdone.
The whole security clearance practice has become a religious ritual that often fails to accomplish its desired goal.
I spent years working in a defense lab with people who were running numbers, on the take and abusing just about any substance imaginable, which is to say just like ordinary life.
This topic is just another demonstration that if you create a system, people will game it.
I have worked with substance abusers who were very productive and with straight-arrow folks who were drones or destructive.
All the formal testing systems seem to simply convince people that the use of good judgment and common sense is a bad idea.