"shall not be infringed."
What follows is my plain English understanding informed by Federalists Papers, Supreme Court opinions for and against, and intellectual writings separate from court opinion, and my own opinion formed by the aforementioned and 7 decades of thoughtful deliberations.
My analysis is drawn from the understanding of the meaning of words, ideas and history, at the time Madison wrote it and events since.
First, let's examine the phrases set apart by commas, which I assume is what the framers intended.
"A well regulated militia," to me means a militia kept in check. I think the biggest concern at the time of the adoption of the Bill of Rights as Amendments was having armed citizens able to resist tyranny from any opposing force, even Local, State or National police and military organizations gone rouge attempting to violate the most basic human rights enumerated in the Constitution.
Secondly, "being necessary to the security of a free state," means regulated by an opposing force of citizens to secure the conditions that allow the existence of a free state. Without an armed force powerful conspirators could become tyrannical and run roughshod, violating every preciously secured right over isolated locales or the entire country.
Next, "the right of the people to keep and bear arms," is the right of a free people to secure, protect, and assure a free state by keeping and bearing arms as necessary; not a militia, but in opposition to unlawful gangs or lawful militia gone bad.
Finally, "shall not be infringed." means precisely what it says. Nothing is authorized that modifies this right of a citizen; not significantly, or not slightly, shall not at all be infringed upon.
A Supreme Court decision established that convicted felons and crazy people should not have this right that the 2nd Amendment plainly and definitively states, "shall not be infringed." I do not disagree that convicted violent felons might be stripped of this right, but crazy could easily be determined by the state to be anyone that opposes the party in power at the moment.
There are lots of mental and emotionally challenged persons that function without danger to the state or other citizens; to strip this right from them without empirical evidence of potential harm to themselves or others, would be infringement which "shall not" be allowed. Tyrants, bigots, zealots could easily select a chosen behavior or affiliation and demonize it often and loudly, saying the poor souls who have chosen badly are crazy and therefore should all be stripped of their 2nd Amendment Rights; imprison them and seize their lands, personal property (guns and ammunition), livestock, and accumulated wealth, without the due process rights assured in the Constitution.
A few examples of groups of affiliates that could easily be demonized are, National Rifle Association members, Meat-eaters, non-Christians, elected politicians, teachers, or American Socialists Party, Green Party, or Radial Extremists Democratic party members, or any identifiable group could be characterized and easily determined to be "Crazy".
Incidentally, I would submit there are several mentally ill persons in Congress in any year, House and Senate; and most assuredly many in the party that nominated them, by any reasonable definition of the term "crazy".
The millions of people who admit to owning guns, and the millions who do not, but use them for hunting, competitive sport shooting, home protection, collecting, or just because they have the right to; have about 400 million working and non-working personal property firearms that have never killed or injured anyone. This estimate does not include the military, National Agency Assault Teams (DOJ, TSA, IRS, NSA, etc.), or State police/militias.
Here is some interesting data and estimates from official sources, not news media or other anti-firearms advocates.
US Deaths by firearms:
Justified Police homicides 2017 - 429
Justified citizen homicides 2017 - 353
source: FBI
Suicides by firearms
2016 - 22,938 CDC
2017 - 23,855; 50.57 percent of all suicides (47,173)
Accidental or unintentional deaths by firearms
2013 - 505
2014 - 461
2015 - 489
2016 - 495
Undetermined reason, by firearm
2013 - 275
2014 - 275
2015 - 282
2016 - 300
Executions
2010 - 1, Ronnie Lee Gardener, In Utah at his request.
Homicides by Firearm, as a crime, or during the commission of another crime.
2016 - 14,415 CDC
Sources
CDC - Center for Disease Control, Deaths, Final Data 2016, tables 6 & 7
FBI - Federal Bureau of Investigation
In no case did a firearm load itself, aim itself, or fire itself. All events absolutely required deliberate human action prior to the resulting death. No unloaded weapon discharged a single solitary cartridge.
