Actually, the granddaddy of libertarian economics, F.A. Hayek, spent his whole career arguing that people are irrational (which is to say, they do not all share the same preferences), and that attempts to shape the economy based on a presumption of the existence of rational utility are doomed. Most non-libertarian economic systems are based on the assumptions that,

1. There is such a thing as rational utility, and 2. Bureaucrats can figure out what it is.