Abstract: The Pareto principle, the seemingly incontrovertible dictum that if all individuals prefer some regime to another then so should society, may conflict with competing principles. Arrow's impossibility theorem and Sen's liberal paradox are two notable examples. Subsequent work indicates more broadly that the Pareto principle conflicts with all non-welfarist principles. This essay surveys these results, including various extensions thereof, and offers perspectives on the conflict, drawing on classical and contemporary work in political economy and economic psychology.