Social contracts are where we establish that people can't do whatever they want. The game rules are merely an appendix to the agreement between people about what we are doing.
And yes, enforcement of social contracts is awkward as heck. I am sorry, but being human is awkward as heck.
Until such time as we have game books that, I dunno... deduct money form the GM's and players bank accounts when rules are broken? Calls the Game Police to confiscate your dice, or something?... enforcement of all game rules is an extension of social contract.