Might kantian contractualism be the supreme principle of morality?

According to Parfit, the best version of Kantian ethics takes as its central principle Kantian Contractualism: The thesis that everyone ought to follow the principles whose universal acceptance everyone could rationally will. This paper examines that thesis, identifies a class of annoying counterexamples, and suggests that when Kantian Contractualism is modified in response to these examples, the resulting principle is too complex and ad hoc to serve as the 'supreme principle of morality'.