Still too broad a range, smoking some weed at 7pm doesn't necessarily make you unsafe at 7am. Zero tolerance is unrealistic and unnecessary for most jobs that drug test.
That, plus marijuana is still illegal in most states. Whatever your personal conviction may be, businesses aren't in the business to turn the blind eye to illegal substance use. They're on the hook for liability.
NPR recently pointed out that if you include medical marijuana this is no where close to true with it being legal in 29 states: https://en.m.wikipedia.org/wiki/Legality_of_cannabis_by_U.S....