Economist Bryan Caplan asked an interesting question on his blog today:

All ideology aside: If the government had followed a laissez-faire policy for the last six months, and output, employment, housing, and financial markets stood exactly where they stand today, what fraction of people would conclude that "Events decisively prove that laissez-faire is a disaster"? Can you honestly give any answer less than 90%?

The ensuing discussion in comments is pretty educational.