On the Second Amendment and the Right of Revolution
There are several reasons some people in the United States support the private ownership of guns. School shootings and the rest are unfortunate collateral damage of ensuring the principle of individual arms can be readily obtained.
The Second Amendment confusingly says
"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."
It is not clear on what arms people can have. Almost everyone agrees people should be allowed to have knives and muskets. Almost everyone also agrees no private nuclear bombs. I like the idea that original intent of the word "arms" means that no weapons invented since 1789 are implicitly constitutionally covered. The current interpretation of the second amendment is a modern one.
In addition to the "well regulated militia" rationale, there are other reasons people might want guns, including:
Committing crimes (some of which is self-defense while doing illegal things)
Over-throwing a `tyrannical' government (which also relates in part to self-defense when rebelling against a well-armed opponent, as well as offense against the same opponent). This is also known as the "right of revolution." It is discussed in this Federalist article.
I believe most gun supporters are, in fact, though most won't admit it, about the last point. That is, their minds foresee a dystopian outcome when a fascist (or communist, but same thing) comes to power and must be resisted by weapons that have yet to be confiscated by a weak liberal regime.
The Civil War is a morally repugnant example of this kind of resistance, in that case by a south defending slavery; but one can equally imagine a world where a slightly less demographically and economically powerful north was resisting imposition of slavery by the southern states.
Or, their mind foresees the US being invaded by a foreign (or alien) army which somehow the military was unable defeat. Having grown up in the 1980s and seeing Red Dawn and V, I have some empathy for that view in principle. In practice, not so much.
Yet, if you are right wing, and believe the previous administration was the illegitimate dystopia that fuels your nightmares, where was your uprising? I missed it. If you are truly anti-fascist, where is your uprising now? You, gun-owners of America, are as well-armed as any citizenry in history. The US government's ICE brown shirts are taking people from their homes and deporting them. Police officers are systematically killing people of color. And gun owners are not systematically challenging them. Hmm. Oh, I missed the part that it was the right of revolution for white people.
Which leads me to the conclusion that over-throwing the US government with the citizenry's privately owned weapons is just not going to happen. Which means, we can strike the justification of needing guns for keeping the government in check. At this point in history, the US government can keep the populace in check, even if armed. At best you can take someone out before being killed yourself. You will not actually win.
The counter-argument is that it is the well-armed citizenry that is keeping the government in check, and thereby keeps it from confiscating guns (and eliminating other freedoms, but those are secondary to the guns). But if that were true, they wouldn't be worried about the government confiscating guns. The reasoning is circular. The reason to have guns is to keep the government from confiscating your guns. If the government could confiscate your guns at any time with a change in legislation, the guns aren't actually buying you your freedom. Instead it is that the government cannot effectively act without the consent of the governed.
Since the 'committing crimes' is also not really a good reason to keep guns, and 'hunting' doesn't require sophisticated weapons, and 'personal self-defense' with guns is only necessary because everyone else also has guns and may be committing crimes, the US should just throw in the towel and follow the civilized world, or even Australia, and more significantly reduce access to firearms.