Don't see a connection...
Ok sorry my statement isn't very clear is it? There are many actions that while legal are not acceptable at work. Here in California there are many many people who have a medical marijuana card. At our high schools it is perfectly acceptable for a student to smoke dope and sit through class stoned provided they have a card. Students just walk off the campus a few feet and light up a joint. The school administrators can do nothing. However if they smoke tobacco they can be expelled.
Would you expect me to hire someone to run a saw or a chipper who is stoned during the workday? Regardless of whether their actions were legal or not I will not hire someone I know is stoned during the workday?
The same goes for carrying a gun at work. (Note: I am a gun owner, hunter, and 20 year life member of the NRA. I have been an NRA member since 1964. I am also a firm believer in CCW laws while on personal time.) While it may be legal (in your state) to carry I would never allow an employee to CCW during the workday. Keep a gun legally in the truck...sure. Carry during the day...no way. Good luck convincing your workers' comp carrier to accept CCW.
As far as drinkig alcohol during the workday, I would fire any employee who did. And I have.
A few other thoughts. I am a supporter of giving ex-offenders a second chance. I have worked with many ex-offenders through Labor Ready, a hiring service who helps people find (mostly low paying) jobs. Around here most x-cons have been encarcerated on drug or alcohol related charges but I have worked with car thieves, burglars, and even murderers. In fact I worked with a triple murderer last summer. I am also a firm believer that everyone has to play by the same rules. If work starts at 08:00 then I demand that you show up ready to work at 08:00. Coffee and donuts while the equipment is being fueled or greased is fine, but don't think you can show up at 08:00 and the start eating breakfast. I have not fired anyone for that but I have given several guys a last warning. Coffee/tea/water breaks during the day... take one when ever you need to. If you leave the jobsite for lunch be back ready to work in half an hour or your pay will be docked and you will likely fired if this continues. If you have to stay 5 minutes after quiting time to work on equipment then you will get paid for your time. If you have to use your own car to run to town to buy parts the you get paid for gas and wear and tear. All safety equipment except boots are provided and if I tell you to wear saftey gear and you don't, well guess what you will be fired.
As an employee when it comes to the workday life is pretty much black or white regarding rules. I try to use common sense and I ask for input. I don't want yes men. I would much rather be told in no uncertain terms that I am doing something wrong. But don't try to bend the rules. No guns, no booze, no drugs. And no talking on the cell phone while you are working.
BTW if you are an employer medical marijuana users are a huge issue. The cards are sold by "doctors" and business is good. Stoned employees and chain saws don't mix.