The fact that the outcome is chosen collectively rather than individually guarantees that a wedge is inserted between the act of choice and its consequences. Individuals do not really choose in the meaningful sense of the term, at least not among outcomes of the process. And the disjuncture here means that no identified individual is responsible for whatever emerges from the selection process. The straightforward logic of opportunity cost does not apply. That which is forgone by the individual’s act of participating in the process, of voting, is not the opportunity loss of one outcome or another.
In this setting, it becomes much less costly for the individual to act in accordance with unexamined ideological persuasions rather than any comparisons of outcome by criteria of measurable interest.
Jim here nicely summarizes a key lesson in Geoff Brennan’s and Loren Lomasky’s brilliant 1993 volume, Democracy and Decision , as well as in my GMU Econ colleague Bryan Caplan’s equally brilliant 2007 book, The Myth of the Rational Voter . This lesson alone – independently of other nails of realism that public choice  supplies for our efforts to hammer down a better understanding of collective decision-making – is sufficient to create a powerful presumption against the notion that political decision-making results in coherent, efficient, or just outcomes. The fact that so many professional economists and other scholars barely, if at all, acknowledge this reality testifies to the still-largely unscientific mindset of too many social scientists. If these social scientists were zoologists, they would all have elaborately mathematized models of the countless wonders that could be performed by airborne goats – but all these models would simply assume that goats can fly.