The mathematically most tractable rationality is the optimization of a transferable utility in a single transaction. Often we wish to behave this way, but often neither our wishes nor our actual behavior can be described in this way. We want to be rational at least in the sense of transitivity of preference, but often we want total ordering. That is a person wants his own preferences to be totally ordered.
Rationality is most feasible in the short run.
It is not easy to define what humanity wants between now and the heat death of the universe. It is also difficult to say what a person wants over his whole life. Consider an animal that has certain drives. It is not plausible to ascribe a utility function to the life of a dog let alone a bacterium. Much is apparent about the welfare of an animal in the short run.