The key word is "unlawful user." A person with an MMJ card (or any person in a state that has legalized MJ for recreational use like CO) can legitimately argue that they are not unlawful users, and that's not a frivolous argument, either. It's a very powerful one that gets to the heart of an issue that our country has struggled with since its founding, the question of where does the authority of the Federal government stop.

After all, if the state has explicitly said they can use MJ, then how can their use be unlawful? States have a general police power to decide what is lawful and unlawful within their own boundaries. The Federal authority only exists where the Constitution has given the national government that authority.

Whether the form is a federal form or a state form is irrelevant - the only relevant question is whether a state law that allows someone to use MJ makes them a "lawful" user vs. an "unlawful" user.

Right now, law enforcement benefits from the ambiguity and that's probably why they DON'T want a court to rule on this. I'll bet the feds would bend over backwards to avoid getting this question to a court because they're afraid a court might rule against them and say that someone who lives in an MJ legal state or someone with a MMJ card IS a "lawful user" which would deprive them of a way to try and limit gun sales.

Incidentally, don't think I'm an MJ user or supporter. I voted against amendment 64 and I still think that all the rosy predictions about how great legal MJ is going to be for Colorado were overstated, and that there's going to be some significant negative effects like increases in petty crime, increases in welfare costs, child abuse and neglect, etc.

But in terms of legalizing MJ being a way to roll back Federal overreach, and for the state to say "screw you" to the feds, I have to admit I kind of like it. There are pot shops all up and down Broadway, and every time another one opens, the options for the feds to swoop in and close them down becomes more and more problematic for them.

In short, all of the states that have legalized MMJ (and I think it's over half of them now) are, in essence, in open (if rather mild) rebellion against the Federal government. It's a "peaceful" rebellion, but it's still a rebuke to the Federal government's authority.