I can see that there really is a social contract, and one that makes perfect sense: You don't fuck with me and I don't fuck with you (the non-aggression principle.) If you think about it, it's what we're taught when we're toddlers.
"Johnny, don't fuck with Timmy's stuff without permission. You don't want him to fuck with your stuff, right?"
"Jenny, don't hit your little brother. In a few years, he'll be bigger than you, and you won't want him whaling on you then."
"Don't touch that--it's not yours."
This is the social contract (and it has its basis in natural law.) The other one is bullshit.