The Federal gov't has made THC illegal, just because a few states have decided to look the other way is moot. At the Federal level the ATF has a requirement listed on the 4473. Saying no while using with a medical card is perjury. Some of the people that get those cards are in a lot of pain and require something. Having said that, there is a bit of a cottage industry pumping those cards out to just about anybody that asks. There are plenty of Drs that will issue a card for the right fee.
Gayle's aunt recently got one and has a couple dozen plants at the house (another reason I will not be visiting again, I like my job). She has had chronic back and joint problems for years. She was on so many pain meds she was unable to function. from what gayle said, she's not taking as many but the pot helps. Guess what? She has a lifetime CCW permit from the state. Her semi-annual requal is a joke. She can barely hold the weapon up and pull the trigger (G26). As long as she gets two out of the mag on a target, anywhere, she passes. She is constantly saying people are stealing from her, most of the time she's misplaced something. She had some people living with her that did steal stuff, money, medications, and at least four pistols that we can identify. One was recently recovered after a robbery. She's a great person, but do you want someone like that with a weapon?
Personally I think that anyone who has a dibiliating condition that requires significant, long-term, narcotic therapy should really evaluate whether they are capable of safely operating firearms, cars, and other machinery. I'm headed down that road and in a few years, hopefully a lot of years, will probably need to make that choice. As much as I like to shoot, if I can't do it without lots of medications that cloud my judgement I don't think it's safe anymore.