This one has become obsolete. When our constitution was created your gun put you pretty equal with the standard individual military opponent. You had a chance. You could make a pretty good run at being alive and defending yourself as an individual. That is all but gone in today's world. even a well armed group of civilians working against military force would not last very long at all, or be much of a seterrent. With our police heavy society the idea of an underground resistance becomes harder also. The tools that allow for finding hidden people and things have vastly improved. In this aspect your gun no longer provides you that same protection. Now if you were to have access to heavy weapons, jets, submarines, missiles, tanks, explosives, and advanced detection and tracking equipment I would think you had a fighting chance. Since the government restricts these things and never gives you access to most of them you are pretty much SOL with your little plinker.
It depends on who is invading. If it were a power that could do something like overcome the US military I would say it would need to also have the power to disarm and lock down the local populace. Yes, in the initial stages you might be an obstacle, but if they are putting down US soldiers and going over better defenses your little gun is not going to be much of a concern to them. I would argue that perhaps such a force that is capable of overpowering the present US military presence does not exist. The reality is that the weapons which would now tear down our defenses would not be fought off by you and your gun. The best you could hope for would be to mount some sort of guerrilla resistance with your guns, which would involve you getting ammo stores before lockdown and confiscation occurred. This might be applicable in the case of massive warfare where they cannot remove your guns.
this is a better argument. Unfortunately it is still not a great one. There are other things which would be cheaper and more effective to implement before a gun. Those things would also be more reliable. For instance an alarm and security system including hard to break into locks and some safes would be an active system that would defend from all attack points, have better perception than you do, and be active more than you are. I am not saying a gun would not have a place, but that there are things which would be more effective to avoid theft or attack that you could do first. A gun does have the necessity of being aimed and fired to work against a determined attacker which is not something you are constantly at the ready to do, nor is it something you can maintain on every attack vector. Also, a gun can be used against you if you are disarmed or it is taken before you can get to where it is. Reliance on it is fail.
Still, being who I am and open to people enjoying recreation I would say recreation is a good reason for us to allow gun ownership. Though I do support restrictions and safety measures I see no reason to deny a law abiding level headed, trained individual to keep and shoot guns for the pure fun of it. All I would ask is we keep them out of the hands of the crazy, criminals, unsupervised children, and intoxicated people. I also think there should be some rules about safety and storage of the gun. But along those lines I do not see a need for any restrictions on what types you can own. If you stay as a law abiding citizen, go to appropriate target ranges or hunting areas, and are not wacked out of your head by either nature or substance I say have at it.