Perhaps one should first make sure we have consensus on what is used by social contract theory.
twistedbydsign99: So I'm wondering what the best argument you guys feel, against the social contract theory, is? I suppose its just that entering into a contract without having to sign anything sorta negates it.
You do not have to sign something to be in a contract. Even if many people think that one "signs a contract". One doesn't, one only affirms the existence of a contract via signature and the signed document is henceforth documentary proof of the existence of a contract as declared within the document.
A contract is an agreement between more then one parties. Such an agreement can come into existence if A states an intention to B. There maybe conditions that apply. With other words if you tell someone you sell item Y for X amount this already would be a contract, if it is accepted and the conditions are to be met. Then there are implicit contracts as well...
twistedbydsign99: Or perhaps that the united states can never enforce a territorial contract on us because it slaughtered the original owners of this land and therefore are by default invalid. Anyone have some clever refutations?
It slaughthered the original owners? Is that a true statement?
Anyway don't forget that warfare is one of the means to gain dominion over a territory just as homesteading, purchasing/exchanging, receiving are donation etc. are. Besides that, I think this would be making a category mistake. Because this only would render the claim invalid, but not the principle. The principle in question would be assuming a legitimate claim to territory and that this claim would result into a legitimate (social) contract over the inhabitants.