I've always understood it to mean pretty much a combinaiton of all of the above. When the majority of the populace is armed, any transgressions in the mores of the time are dealt with swiftly and severely, and sometimes the "wrong" person comes out ahead. Therefore, you should mind your manners, unless you want to start something that could end up in your own demise. Not just that, but because there would be little true criminality (out in the open, anyway), most people would feel safer, and would be more inclined to be polite, and helpful towards strangers.
Double Nought:
There are many interesting ideas for governance to be learned from Heinlein's works. For example: In Starship Troopers, the entire civilization is governed by former servicemen and women. Not because they're smarter, or more able to govern, but because they've shown (through the act of volunteering for a tour of duty in the armed forces) that they place the welfare of the whole as greater than that of the individual.
In several novels, the idea of an armed society, ready to mete out justice in the stead of any organized government exists. In some stories, religious majorities attain power, and become corrupt, requiring them to be overthrown. Over all, there is a strong libertarian trend. In every Heinlein story of space exploration there's an attitude of "I'll take care of what's mine, you take care of what's yours, and we'll get along fine." Some notable quotes:
Lazi, you've heard me say nine thousand and nineteen times that we do not carry weapons to give us Dutch courage. If a gun makes you feel three meters tall and invulnerable, you had better go unarmed [...]
--Lazurus Long, Time Enough For Love, pg 435
We don't shoot cops if there is any way to avoid it. Safer to kiss a rattlesnake.
--Lazurus Long, Time Enough For Love, pg 435
Mary, if there is anything I have learned in the past couple of centuries, it's this: These things pass. Wars and Depression and Prophets and Covenants -- they pass. The trick is to stay alive through them.
--Lazurus Long, Methuselah's Children, pg 24
He was aware of the present gentle custom against personal weapons, but he felt naked without them. Such customs were nonsense anyhow, foolishment from old women -- there was no such thing as a dangerous weapon, there were only dangerous men.
--Methuselah's Children, pg 27
Besides, as my boss says, with all governments everywhere tightening down on everything wherever they can, with their computers and their Public Eyes and ninety-nine other sorts of electronic surveillance, there is a moral obligation on each free person to fight back wherever possible -- keep underground railways open, keep shades drawn, give misinformation to computers. Computers are literal-minded and stupid; electronic records aren't really records . . . so it is good to be alert to opportunities to foul up the system.
--Marjorie Friday Baldwin; Friday, pg 5
Sick cultures show a complex of symptoms such as you have named . . . but a dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for other in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.
--Dr. Hartley M. Baldwin; Friday, pg 242