But "rational" and "fully informed" isn't enough. If I encode prices as a 3SAT problem, then your "rational" and "fully informed" person will be required to solve a (thought-to-be) too hard problem in order to do the efficient thing.
Therefore, either you can solve such a problem efficiently (and P=NP) or the idea that all you need is rationality and information is false.
Therefore, either you can solve such a problem efficiently (and P=NP) or the idea that all you need is rationality and information is false.