We tell these people about "social contracts" then smirk when they raise the common sense objection of never signing such a contract in the first place.

Of course a social contract is not at all the same as a real contract, a social contract is not a document that you sign, it applies to you whether or not you ever consented to it. But when language that seems to conflate the two is used to persuade people who don't really have a firm grasp on the way the world works, it seems cruel to laugh at their confusion.