Gun Control & RKBA

The law that applies to situations where State and Federal laws disagree is called the Supremacy Clause (part of article VI of the Constitution). https://en.wikipedia.org/wiki/Article_Six_of_the_United_States_Constitution#Supremacy

The supremacy clause contains what’s known as the doctrine of pre-emption. It states that the Federal government wins in the case of conflicting legislation between State and Federal laws (and Constitutions). If a Federal and State law contradict, and when you’re in the State and you're not challenged, you can follow the State law. But if the Feds decide to intervene - as was the case with the South's Jim Crow laws - it's game over.

Whenever there's a conflict between a State law and Federal law, it's the Federal law that stands. For example, those egregious Jim Crow laws (which forced the U.S. Gov't to step in) I've mentioned above, same-sex marriage laws, and the Federal regulation prohibiting the use of medical marijuana, as you've pointed out. Even if a State regulation allows it, but it's challenged in a Court of law, the Federal law prevails.

I'm truly surprised that far too few Americans know this.

I don't know if the lawsuit was without merit. I haven't seen or read all the evidence the Plaintiffs wanted to present. The PLCAA was used to immediately strike down the lawsuit before the merits were litigated. The judge should've just allowed the suit to move forward and let it fall for lack of merit, if that's the case. But that's not what happened here. The PLCAA was used to throw the suit out. And that's a shame.