Starting (as one always should, since it's an axiom) with the self-ownership axiom, two things follow, about guns:
1. Everyone has a right not to be shot, except when threatening someone else; and
Are there exceptions to #2, such as lunatics and young children? - no. In the case of kiddies, parents will make sure they don't have a gun until responsible enough to control it (any more than they will serve them Bourbon and for the same reason) and in that of the mentally ill, medical guardianship will in a similar way protect them from irresponsible use, which could otherwise bring fatal blowback.
Otherwise, the right to own a gun is natural and absolute, and no third party, such as a government, has any right to infringe it. In the USA that is made explicit in the supreme law; (a) no such right of infringement is delegated to government and for good measure (b) government is expressly forbidden to infringe it, by Amendment 2. It is good that the new President has made clear that he understands that. This applies to the FedGov, and most State governments have in their Constitutions a similar guarantee of non-interference.
Those clear, solemn and binding promises are daily violated all over the map, but they are there and they are valid and the violations serve only to confirm that no government guarantee is ever worth the paper on which it is written; and so that government is an institution in urgent need of abolition.
So much for the right to own and carry a firearm; but you and I also have the right to own and carry any other artefact acquired by honest exchange (or in-house construction) and we'll not buy everything we could. I don't have a motor cycle, for example, even though I have a right to own one. Hence a question: what's the value of gun ownership? Put differently, is it a good idea to exercise this particular right? What benefits do guns bring?
First and most obviously, they furnish a frequently effective method of self defense. Not only can a handgun be deployed quickly in an emergency, its very presence - even its possible presence - acts as a powerful deterrence to krime. That is all true, and on its own will suffice to keep gun ownership popular; police response times may be fast, but none are as fast as the few seconds needed to draw and aim a gun.
That advantage of gun ownership is, however, limited. It's good for defense in one-on-one conflicts, when threatened by one individual kriminal, but not so useful when faced with several, acting with coordinated force, when the attackers are themselves well armed and prepared with protective gear, as in the case of a government SWAT team. It may be possible to take down a couple of them, but you the defender will certainly die; they are expert at applying concentrated force. Witness for example Randy Weaver; he killed one of his attackers and did survive, but suffered the agony of losing his dog, his son Sammy and his wife Vicki.
Would they be effective in a "survival" situation? The premise is that government has melted down (quite possible) and while collapsing has taken with it the infrastructure of electric power and food distribution, leading to swarms of desperate, starving people rampaging to steal the supplies of those who have prepared for such a contingency. Yes, they may be effective. It would be a deep tragedy, though, to have to kill fellow-victims of government rather than the instigators of the mess.
A second reason to own a gun is the sheer fun of target shooting, and I enjoy that and can see no downside to it.
A third reason is to kill pests that would otherwise destroy a farmer's crop or animals; and though perfectly valid this would apply only to 2% of the population.
A fourth is to hunt food, and I must admit to some ambivalence here. Since I'm not a vegetarian I can't argue that killing animals is immoral, but there seems something wrong in destroying often beautiful creatures doing no harm to any others - especially if the killers do it just for "sport." Farming cattle or fish is a bit different; the farmer is creating life as well as ending it. But in a pinch, when survival is at stake, yes of course hunting is morally valid.
Sometimes a fifth reason is advanced, to own gun(s): it's said to be a way to defeat government. The thinking here relates to the successful Revolutionary War; the existing government was overcome and militia (plain people, often farmers, armed with their own guns) were a key factor in the victory. Notice, this is not the same situation as what prevailed at Ruby Ridge, or Waco. The idea here is that an organized force harass government armies, taking the initiative as guerrillas. It worked in 1781; why not again?
This is, I suggest, flat wrong. First, although militia were important in that war, they were far from decisive; the Brits quit only when cornered by a conventional army and the French Navy. Second, that War did not defeat government at all; it merely kicked out one government and put another in its place. And third, although guerrilla-type raids may motivate occupiers to give up and go away, and although they would be used to defend the coming free society if ever some government was so foolish as to invade it, violence is very far from the best way to abolish the existing one, as required by the fifth paragraph above.
I showed the reasons for that in What Might Have Been, but a quick summary is that it's silly and immoral to use the very weapon of government (violence) to abolish government - even if it could be done, which is a big question: Francis Tandy's insight was that if you have enough support to win a violent war against government, you don't need a violent war against government. All you need do is to stop helping the tyrant, and he will collapse. To "withdraw support" means to stop working for it, and that in turn means learning what a crock of lies and depravity government truly is, and that means some homework. TOLFA provides it.
So, how important is it to own a gun? Somewhat, but not as vital as some suggest. A gun is fun, in some circumstances useful, and in rare ones a life-saver; but as a means of ending the government era, it's a non-starter.