Ok, so you need to explain why there is moral obligation to register your guns with the state, and if that moral responsibility applies to all other weapons (knives, etc) as well.
There is a moral obligation to register weapons including firearms so that there can be a clear chain of ownership of legally owned weapons/firearms in order to figure out how illegally possessed weapons/firearms came into the possession of those caught with them. By tracing an illegally owned weapon back to its last legal owner, authorities can better figure out how guns are moving from the hands of legal manufacturers and owners into the hands of criminals. Such registration will also help track interstate movements of illegally trafficked firearms and make it much harder for owners to voluntarily alienate firearms to black markets.
Anything from a rock to a dog can be a weapon so the first threshold is to exclude improvised weapons from registration. Knives, axes, picks, hammers pitchforks, etc. should be excluded as they are tools which have many non-weapon uses and so can also be left off from a weapons registry. Low powered bows, light crossbows, stone bows, slings, slingshots, etc. probably fall below the threshold of potential lethality to require registration. High powered reflex, composite, long and mechanical bows plus heavy crossbows should be registered just as firearms should be. Swords, spears, pikes, javelins, maces, morning-stars, military flails, military axes, military picks and hammers, bills, halberds, etc. should be registered as their primary purpose was and is to serve as weapons. Rifles, shotguns, handguns, flare guns/launchers, launchable grenades/flares, sniper rifles, etc. should be registered. Semi-automatic rifles should be restricted to owners with proper training and good reputation who are vouched for by other gun owners in good standing themselves. Submachine guns, machine guns, Gatling guns, rifle grenades, explosive or incendiary grenades, attachable grenade launchers, automatic grenade launchers, mortars, recoilless rifles, functional artillery, functional armoured fighting vehicles, LAWs, MAWs, ATGWs, MANPADs, mines, etc. should be prohibited weapons and not be owned by private citizens.
No. This: "there is no right to privacy built into the second amendment" is a legal argument, which is completely irrelevant in a post about moral responsibilities.
Here is the text of the second amendment: “A well-regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.”. Where is the reference to a right of privacy/anonymity for gun owners here? please point it out! if you can. It simply doesn't appear in the second amendment. Fact. In fact the amendment mentions a well regulated Militia which can only be well regulated if the militia commanders and quartermasters have a clear notion of who owns what firearms. So implied in the second amendment is that weapon ownership must be disclosed and can be regulated to better serve the needs of the state militia.
Once again, you invoke legality into a question about morality. Let us suppose that there is a registry of gun owners, and the government (state or federal) sends cops out to confiscate firearms with proper warrants. Do gun owners in that situation have a moral responsibility to obey and turn their guns over to a democratically elected government?“
These are moral choices which each gun owner must answer for themselves with the full understanding of the consequences of whatever action those owners choose. My position is that you fight state overreach of power by peaceful and mostly legal means (civil disobedience being the edge of the envelope) and do not resort to violence unless your life or those of your family/neighbours are directly and imminently threatened by the state agents' actions. As TurtleDude has already said in this thread, he believes very differently from my reckoning.
What I can say is that folks have been registering land, buildings, deeds, wills, trusts, mineral claims, vehicles, pets, children, stocks, etc. and no one including the state has seized them en masse in modern US history without good cause, proper political process, prior warning and legal due process. So the notion that armed agents of the state are going to turn up at your door to confiscate your stuff without just cause, legal writ, prior warning and due process, just because "democracy" told them to do so, is absurd to me. If you're really worried about such a scenario, then secretly cache weapons and ammunition securely where the authorities can't find them and then fetch them after the initial outrage in order to fight off the storm troopers of the dystopian state of your nightmares.
Cheers.
Evilroddy.