As a card carrying member of the NRA and avid hunter/shooter/cpl holder I am certainly pro firearm. But until the federal marijuana and/or gun laws change, there will be issues with federal gun laws and marijuana. You have to remember marijuana is not legal, the MMMA just blocks prosecution under state, but not federal, law.
The other issue is that the second amendment deals with 'the people' but 'individuals' can be specifically denied the right to own firearms for cause. Being a felon is an example of a class of people that not only are denied the right to have a firearm, but even to vote. Under current law, there is an argument to deny the right to have firearms, but in some cases, that has been overcome in court in specific cases (there is a federal appeals court ruling out West that applies in that district, but the supreme court would not hear the appeal).
In the case of my patient, he did have a card but was able to prove he wasn't using it, and won his case.
Dr. Bob