Here's the thing though:

can spend 2 weeks in a psychiatric ward for hearing voices in his head telling him to shoot up the said Militia

They can't, it is already a federal law that people who are IVC'd (this guy) are prohibited purchasers and they are supposed to take the guns and input that into NICs, but someone didn't do their fucking job. Has nothing to do with the weekend warrior ~~militia~~ branch of the US military either, that applies to everyone, federally, as it is a federal law.