Are social contracts (such as the Constitution) legitimate and allow people to be bound by them just by being born in the country?
Yes. For two reasons:
Hobbes articulated it best, but I can summarize him with the argument that having unlimited liberties (essentially, no restraint on your character) leads to anarchy because there is no property, no confidence in societal order. An anarchy does not have these things because property is merely that which you can hold onto with a weapon (force and violence) which means that there is no certainty in the stability of day-to-day life. These things we take for granted like rights, property and the ability to plan for a future investment dissipate when life is about survival.
Therefore, he explained, that at some point we make a choice to create a government. We choose to give up some of our freedoms (like the freedom to steal, kill, pillage, etc.) in exchange for property, the ability to have stability and rights. A government is a contract between the governed and governing, the governing being representatives of the people with a sacred duty to uphold their wishes as well as protect their rights - civil servants almost.
So from this perspective, a social contract is legitimate because without it there is no civilization. There is only barbarism.
The second reason is actually quite simple: convenience. A child is not a voluntary thing, that is to say you do not volunteer to be born. You do not have a choice where you are born. You can’t even appreciably understand civics and law until you are an adult. Therefore, you cannot sign a contract. However, you exist in society. How then can you exist in society if you cannot consent to a contract? Do you live in a bubble away from everyone else? No. Humans cannot develop that way. Does someone else accept the contract for you? Yes and no. By choosing to birth you in a nation, they are signing you to that nation, but they cannot take responsibility for your actions IN FULL, only in part, because you are your own agent. When you grow up, you MAY CHOOSE to exit the social contract. That is the important part - you may choose to leave.
I don’t view the Social Contract as be all end all. I tend to like the idea of Lysander Spooner (i’ll provide more information on him) who wrote “No Treason”. He argued that since the United States of America decided to force war on the Confederate States of America the Union had violated the Social Contract and made it void. He also pointed out that Federal Government is established by a legal contract between States not the people since the people did not sign the Constitution. So the Federal Government is assuming it has the consent of the governed and this does not meet the burden of proof for a valid contract in a court of law.
You can read No Treason here:
Now Lysander Spooner was an Abolitionist and a Socialist later in life. His major work The Unconstitutionality of Slavery is still quoted by the Supreme Court in decisions. Spooner also created the American Letter Mail Company which competed against the Postal Service. He drove the price of mailing something from 18 cents to 3 cents before Uncle Sam forced him to close down.
He also supported blacks killing anybody from the South no matter if they were slave owners or not. Great guy…really.
You are missing the scope of the social contract. It isn’t merely about contracts between governing bodies, but applies to the citizens within a government. Therefore it cannot be rendered void by a civil war, or by states’ signage. We have a constitution and a bill of rights that we consent to, this is the contract. We have a government ONLY because we consent to it.
The term “social contract” refers to the belief that the state exists only to serve the will of the people, who are the source of all political power enjoyed by the state. The people can choose to give or withhold this power.
With that definition the people can change the social contract, in the US via amendments.
Some people want to change the contract via violence today. Some want to reinterpret the contract, expansion of government is a great example. Few want to change the contract via the rules of the contract as it’s to much trouble.
“We the people…”
Our government was established by the free choice of its people and required to serve the people, who in the end have sovereignty, or supreme power to keep or get rid of that government. Our government has lost it’s way as it no longer serves the people but reigns over the people.