I found this in my daily Quora email this morning, and I loved the historical context so much that I thought I would share the answer here.  The answer was provided by Brandon Ross, JD who, according to his Quora bio is an attorney who has spent 10 years as an NRA instructor, 35 years owning guns.

If ex-felons cannot own firearms, why is it not considered infringement […]

Who said it’s not? You’re missing a subject who is doing the considering.

Many ex-felons do very much feel that it is an infringement of their rights.

[…] of their rights (shall NOT be infringed) under the 2nd amendment?

The Supreme Court has held that “the right to keep and bear arms shall not be infringed”—despite no language providing this power—does not prohibit the federal government from infringing the right to keep and bear arms where governments have enjoyed that power for unstated, historical reasons.

Since Heller, I have viewed this static position on the scope of the Second Amendment as a bit disingenuous:

1. Historically, states and municipalities had all kinds of regulations which infringed on the right to keep and bear arms. Rather, the Second Amendment (in the beginning) only restricted the federal government. States could make all the rules they wished. And they often did.
2. Historically, there were additional groups of people who were, from time to time, also deprived of the right to bear arms. e.g. Catholics, vagrants, etc.
3. But, when the 14th Amendment passed, states were “now” forbidden from denying its citizens equal protection of the law. (I put “now” in quotation marks, because at the time, the Supreme Court did not accept this argument; the Supreme Court said that was never the intended function of the 14th Amendment. It wasn’t until about 60 years later—maybe the 1920s or so—that the Supreme Court started to change its mind.
4. At the same time, that this doctrine of “the federal government may stop states from doing all kinds of things under the 14th Amendment,” the federal government also increasingly took on the powers to do what the Second Amendment forbids.
5. There difference is that felons have no “continuing protections” of their civil rights upon conviction. At old common law, if you were convicted of a felony, you were often not long for this world. Felonies were often only dangerous and violent. Your felony conviction was a kind of “civil death”—and there was no purpose for you to have any weapons while you were awaiting execution.
6. But this changed. Instead, of killing anyone and everyone, the focus become, ostensibly segregation, punishment, correction, or rehabilitation. So, most people would be convicted of felonies, and then be returned back to society. Yet, the old doctrines of their “civil death” remained. Remnants of these doctrines still exist today. e.g. Until recently, an 80 year-old former felon could not vote in Florida for some felony he committed when he was 19.
7. But because felonies no longer merit such regular, bloody punishments, there has also been a massive proliferation of felonies—as legislators mint new ones quite regularly. While these new crimes are created casually, not much as changed as to what “felony” means. —Or even “ex-felon”. Or how you you go from one to the other. There is no consensus among legal authorities, and little desire to address that.
8. While there are many non-violent felonies now, the Supreme Court justifies the position that infringement is justified because the person has demonstrated that they will violate the law, and so they cannot be trusted with a firearm.
9. Except… this has no textual basis in the Constitution. The Second Amendment only states that the federal government cannot infringe upon the right to keep and bear arms. Nor does it provide for any permanent loss of any (To get that, you have to read things into the Constitution which are not present.)
10. So, even where a state partially restores an ex-felon’s rights to possess firearms, federal law looks at that and says, “If there is an limitation under state law, then there is a total ban under a federal law.” But, this is impossible to incoherently justify under the text of the Second Amendment.
11. Effectively, this old doctrine has found a work-around to deprive large groups of people of their civil rights: Declare a new felony. If they violate it, their rights go away, for [mostly] good. Yet, that’s the sort of mischief constitutional protections exist to guard against.
12. Because the constitutional rights of felons—or ex-felons—simply aren’t a priority for most people to concern their time and energy with.

— Brandon Ross, Quora, July 11, 2022

I think I would like to add a couple of things minor things to this.

It is true that if you had been charged and/or convicted of a felony in this country, it was more likely than not that you were either about to be executed, or would die serving a life sentence in prison without parole.  In those days, almost any sentence in prison had the potential of being a deadly one, regardless of health and age.  Most people didn’t survive more than a year or two in a prison before succumbing to disease, and or violence.  So if you were a “felon”, you not only would not have a ‘right’ to a weapon, you also no longer had a ‘need’ for one — because you were already considered “dead” in the eyes of the law.  If

you died in prison for any reason, it was no big deal.

Felon vs Ex-Felon.

You are considered a ‘felon’ if you have or are in the middle of committing a felonious crime and you haven’t been caught, tried, and/or convicted yet.  If you are serving time for a felony you are considered a ‘felon’.  But the moment your sentence is satisfied and completed, then you are no longer a ‘felon’.  You would be an ‘EX-felon’, with an emphasis on the “EX”.  Former.  Previous.  Was once was…

A felon or ex-felon is no more or less disposed to kill someone than any other person on earth.  Most people who kill other people have never committed a crime prior to that.  So the reason(s) for denying a felon (and by extension and ex-felon) any rights at all has NOTHING to do with what that person might or might not do with that right, it was just that a felon would be stripped of their rights simply because they were already considered “dead” in the eyes of the law.

SHALL NOT BE INFRINGED.

The US Constitution, written by people who had almost zero concept of firearms in today’s context, felt that one of the most important rights that any individual had to survive in this world was the human right of being able to defend and provide sustenance for themselves.  It is important to note that the words “firearms” or “guns” do not appear ANYWHERE in the US Constitution.  The Second Amendment was more general:

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.

“Arms” could be any kind of implement that could be fashioned into and/or used as a weapon.  The colonists used a variety of different weapons including muskets, pistols, rifles, long rifles, knives, bayonets, tomahawks, axes, swords, sabres, pole arms and cannon.  Most of them weren’t equipped with actual firearms, so it was basically anything they had — they used.

When they were deciding what to include in the Constitution, the concept of “Rights” wasn’t included in the final draft that was signed and submitted to the states for approval.  Virginia refused to sign unless there was a “Bill of Rights” included with the Constitution, hence the reason for “Amendments”.

The Southern states wanted to keep their “slave patrols” to chase down runaway slaves.  George Washington, et al, were against the idea of having a ‘standing army’, so this is where the ‘well-regulated militia’ entered into the bill of rights.  Oh, and because America was still basically an unexplored “frontier” fraught with savages and other unknown dangers, it was probably a good idea for people to be allowed to arm themselves.  Oh, and it would be nice to hunt for supper…

Felons would never have to worry about such things — because they were dead men walking.  Making a law that denied dead people their “rights” would not be “infringing” on anything.