A long philosophical discussion sounds fascinating, but I lack the time.

It is, also, unfortunately (most unfortunately, for I, too, enjoy the work of Locke, and Hume, and Hobbes), a bit irrelevant. Because as you've observed, nost people don't interest themselves in law, and don't read the various books, the various documents, etc., that bring it to a consistent philosophy.

The governing philosophy in America today is one of the elected over, mostly, the ignorant. Any practical approach we take to understanding how things work in reality must factor that in.

To address a few concrete points:

-) We have a country where circumstances matter and alter our interpretation of law. That's why we have courts. There is some flexibility and some mitigation (especially around punishment), though the law acts as guidelines. But under almost no circumstances does the law flex as far as "I withdrew my consent to be governed, therefore I cannot be justly coerced by this court or this government." I'm thinking of 'sovereign citizens' specifically, and they in general wind up in prison (unless they use force to make it inconvenient to apply counter-force, which is rare and risky, since one cannot guarantee the various arms of the US government will stay their hands at application of force).

-) We are a country that was founded in breaking the existing law, this is true. When I said "The social contract is not lightly broken. If one breaks it without a plan for an alternative that can be at least as powerful as the previous arrangement..." the fact that the Revolutionary War succeeded is what I meant by 'at least as powerful as.' Contrast the Civil War, where the South attempted a similar feat and failed (and Reconstruction after, where the North over-extended by attempting to enforce federal law and, arguably, also failed).

-) Freedom to dissociate

... is generous but limited. One cannot practically escape a murder charge by fleeing to the nearest mountain-top. One cannot avoid shared responsibilities like runoff abatement by declaring oneself a sovereign country within the US territory. And we have very specific carve-outs for protected classes of individuals where if we associate with anyone for a purpose (such as employer-employee relationship), we are banned from basing that association on certain qualities, such as gender or skin color.

-) Name two people in authority who have broken the social contract

Well, there was Richard Nixon, who stepped down before being impeached for using his Presidency to bug his political opponents. A judge in Pennsylvania was sentenced to a couple decades in jail for a bribery scandal (https://www.npr.org/sections/thetwo-way/2011/08/11/139536686...) which led to the overturning of dozens of convictions because the process was corrupt. But the unrest right now is related to police authority and support for said authority. Depending on how you slice it, the blame spreads around here; to my mind, some blame is on police for acting as they do in the moment, and a lot is on training and policy for telling police their actions are correct (in contrast to the person-on-the-street response; video evidence has made it hard for people to viscerally turn away and assume police are "just doing their jobs" when they see how policing is done and they contrast it with other countries).

-) How does America treat black Americans? I know I am exceedingly polite towards them. Also, why do you call them "black Americans" and not "Americans"?

This is not something I will invest the time to explain to you here, but I suggest, if you are American, you seek out answers on this topic. There are open riots and civil protests on this topic right now; it's a good idea to be educated on what that fighting is about.

-) what happens to a society, a free society -- when it violates one or more of its founding principles?

It depends on the nature of the violation. But to my mind, we're currently on America 3.0. So major changes can be made and major founding principles compromised without the destruction of the society. Societies can change.

Beta version was the Articles of the Confederacy. They didn't pan out because, fundamentally, they didn't address the practical issue of how to pay for a continent-sized federated government.

Version 1 was the US Constitution, as initially written: main document, 10 amendments out of the starting gate. A hell of a piece of work, but riddled with contradictions and compromises (including, most glaringly, the treatment of enslaved people as 3/5ths a person for the purposes of naked horse-trading over the power of Northern v. Southern states).

Version 2 was after the Civil War. The contradiction that glued two culturally-and-morally-disparate halves of the country together broke down. One half the states tried to declare themselves out of the social contract, and they were "informed" via most brutal force that it doesn't work that way. The country passed laws to make formerly-enslaved black Americans full citizens (but those laws were not universally enforced, and part of the reason we can speak of "black Americans" vs. "Americans" is the law did and the enforcement of the law still does treat them differently). Still, America 2.0 had 3 stark changes from America 1.0: No slavery, full citizenship of black American former slaves, and a clarification that the federal government has authority to use force over the states to ensure the civil rights of all Americans.

America 3 came after the Great Depression and expanded the federal authority over civil rights to the economy. Whereas the authority to regulate interstate trade was understood in the original Constitution, the New Deal established federal authority to regulate intrastate trade as well, because economies have nation-spanning impact. Thus if the government sets a price floor for milk, Kansas can't just ignore it in all sales from Kansas dairy farmers to Kansas consumers. It's less talked about than the changes at the Civil War, but the re-interpretation of federal authority that let the Fed unify the country to pull out of the Great Depression persists to today, in the authority of everything from the ATF to the EPA.

All this to say, a nation that violates its founding principles isn't doomed. America has violated its recognition of the right to own slaves and the right of intrastate fully-free trade and been stronger for these changes.