i dont smoke pot, never have, but I surely support the rights of employers to have requirements for what drugs their ppl use.
if I'm running an airline, I sure as hell don't want some 'medicinal pot' user running the air traffic control. Sure, he might be slick enough to convince a doctor to prescribe it... but stoned people may not be at 100% when it comes to making decisions.
For the average guy running a plumbing business in a competitive market, with 5 employees... Would you rather have 5 employees who don't use weed nightly, or 5 guys who use it? Plain and simple, who do you prefer?