My opinion: Weed is so ridiculously easy to get, most everyone who wants to smoke it does. Maybe not as frequently as they would if it were legal... There will be, of course, some who do only if it's legal, but I would be highly shocked if it were a significant number.
This statement assumes that legalization translates into employer acceptance. I'm guessing many employers would still retain (or newly implement) policies regarding employee use. The impetus to abstain would largely remain in place.
For the record, I haven't used marijuana, and don't plan on ever using it, but it's ridiculous that we not only turn away a huge tax revenue opportunity, but waste millions fighting a futile battle against it.
Not trying to argue against legalization or anything, but weed isn't ridiculously easy to get for everyone. You have to know someone to get it. So if you aren't a smoker already, or connected to smokers, it's not easy to get. You get argue legalizing it could make it easier for people who aren't connected to smoking in anyway to start smoking.