Quoted:
Just on the surface I don't understand how something that is common practice in one state, can be a 2 year+ felony in another. Can you name anything else like that?
I am sure if the supreme court got to it it could easily be overturned via the commerce clause if they chose to.
Running a medical marijuana dispensary will net you differing results in California than in Georgia.
The big difference to me is that there is no Constitutional protection supplied by the founding fathers for stoners at the federal level, (if there was, the Constitution would be unfinished, and smell of Cheetos) but there is supposed to be Constitutional protection for keeping and bearing arms.
"Headache/glaucoma weed" should be a state issue, carrying your personal defense piece should not. This does need to change.
Still, it does not take an amazing leap of thinking to say "I'm going to New York City, they hate guns, I'll leave mine locked in the trunk/at home/melted and turned into a small statue of Lady Gaga. " unless you wanted to do a bit of jail time while providing a real world case that would probably not get to a high enough court level before you were released from jail.