The problem is that a drug test can get you fried for marijuana up to a month or more from the last time you smoked. If smoking gets you messed up for like four hours (just guesstimating here, because the good part wears off after about an hour or two,) you should not be getting fired over having smoked some 720 hours ago.

Nobody thinks people should have the right to go to work high, just like nobody thinks people should have the right to go to work drunk. That's not what anyone is implying here. It's that you can go to work 100% totally as sober as the day you were born, and you can get tested and canned for having smoked on your off-time previously.

This is regardless of whether or not you are responsible, like any responsible drinker would tell you, and put a full night of sleep between smoking/drinking and going to work. That's why it's a problem, because states are legalizing recreational use, then employers are turning around and fucking their employees anyway citing federal laws. Nobody wants stoned crane operators.