Read the constitution. It provides for calling up the militia to defend against invading armies and navies. It provides for letters of marque and reprisal so that civilians can capture enemy warships. Then read the second amendment. Read the Federalist papers where it's pointed out that no standing army could hope to win against a militia that is similarly armed. Read statements of the founders from the time period when the constitution and the bill of rights were ratified. Their concern was whether the people would always be armed heavily enough to defeat any army on earth (including our own), not that the people might get too many scary weapons. Square that with disarming the people or even placing limits on what weapons they should have. An honest originalist reading of the constitution may lead to the conclusion that we may need an amendment to ban civilian nukes.
How 'bout civilian nukes, chem and bio? I'm willing to take a chance on HE, but NBC is a little long lasting in its effects...