I'm talking about your actual work experience. How much difficulty do you have spotting impairment when an employee pops a valium/xanax/percocet/chugs a bottle of cough syrup/etc? How are those different than MJ? Except that MJ smells much more.
So if legality doesn't really matter, why bother keeping it illegal?
Like I said... my only actual work experience was with an MJ problem, and that's germane to this thread. I wouldn't consider myself qualified to say how people react under those prescription drugs as I have no experience with them. When the company tested for drugs we all had to produce documentation if we were taking prescription medicine, and other than cough syrup I've never had any of the ones you mentioned.
Legal is what the law says it is, for whatever reason leadership chooses to use. They are involved in the MJ question for thier own reasons.