I remember an interview with a large worldwide American company where they asked an HR executive why they only drug tested American employees. Her response was that only the Americans would put up with it. Land of the Free, indeed.
I objected to such testing as invasive and unnecessary when it first started. I am not a drug user--I don't even drink.
However, I work in the oil industry, and I have to note that serious and fatal accidents dropped off significantly after such testing started, along with increased safety awareness, lockout/tagout procedures, and a host of other programs designed to improve safety.
I think the original intent was to mollify insurance companies, but the bottom line was that the industry became more professional, fewer people got hurt or killed, and drilling costs dropped as a result of all that. That's just on drilling rigs.
You can still work at a number of jobs that don't drug test employees, but they simply don't pay as well.