Democracy, augmented with some anti-majoritarian safeguards, is a reasonable way of organizing society on a basis that generally advances overall liberties, and social-contract theory provides a reasonable philosophical basis. Libertarian freedom-of-contract is essentially a right to indentured servitude with only the barest attention paid to anything resembling actual real-world liberty or genuine consent, and only people who are either primitivist hippies living in the woods, or malicious exploiters, promote it as a fundamental good. And also anyone who disagrees with this paragraph is dumb.
Anyway, technologue has a point in suggesting that the "social contract" is worthy of skepticism. And I, for one, will join him/her in rejecting the notion of nebulous implicit contracts of this type. When considering this, I'm reminded of what Thomas Paine said about the absurdity of the dead being able to bind the living.
It's the living that bind the living.
Specifically, previous but still-living generations. No one comes of age in a vacuum. If you inherit the benefits (or situations) of the previous generations, you don't just inherit the good stuff, you inherit the debts of the previous generation as well.
Looking way, way back, one can say that the first settlers in a given region might have formed a consensual contract, and the "social" contract is what each continuous generation inherits.
2. ???
3. Declare victory.