Turning past the text â€“ the purpose of the Second Amendment is self-defense. Limiting people to one gun fundamentally jeopardizes self-defense in the event the gun malfunctions, is dropped, etc. The best way to evaluate the seriousness of such concerns is to look to whether police and military personell carry multiple weapons, i.e., whether this is a done thing in contexts where regulation is not an obstacle. This of course is also the leading way of thinking about what kind of weapons can be banned. This is partially an empirical question; I donâ€™t know the answer. The non-empirical part what the threshold must be â€“ how many cops have to carry weapons to make this normal.
Some very good questions. I’ve long advocated that the courts need to evaluate police use to determine the scope of the constitutional protections, the police being situated similar to non-police citizens. That can become difficult. Are machine guns in common police use? Increasingly this is so. I think a reasonable standard would be that citizens can have anything the police can have, subject to the same or similar restrictions to police. This would also tend to serve as a check on the militarization of police forces, since they’d have to accept that issuing “special equipment” to cops means Joe Citizen has a right to access to the same. But we can always imagine far better constitutional regimes than the courts would ever be willing to implement.
UPDATE: More here.