Knowledge of Self-Interest: An Alleged Critical Assumption | Murray N. Rothbard
" It is the popular argument that laissez faire, or the free-market economy, rests its case on the crucial assumption that every individual knows his own self-interest best. Yet, it is charged, this is not true of many individuals. Therefore, the State must intervene, and the case for the free market is vitiated."
"The Perfectly Wise Individual is a straw man created by the critics of the theory, not implied by it."
From Power and Market, chapter 6
Full text available http://mises.org/rothbard/mes.asp