In my experience, alcohol and alcoholics are a far worse problem in most work environments than drugs. Pot, in my experience, doesn't give you nearly the hangover that alcohol does.
I'd be far more concerned about the airline pilot who got drunk out of his mind the night before than the guy who took a couple of bong hits.
But, I will agree with you on this point: someone who isn't willing to quit for a couple of weeks so that they can pass a pre-announced or pre-scheduled drug test probably has a drug problem. In that sense, a drug test is kind of an intelligence test.
