Yeah, I used to believe that, because it was such a neat theory and Ayn Rand's Atlas Shrugged seemed so right. (I was a teenager.) Life has convinced me otherwise. There's a sweet spot (which probably moves over time), but free-market absolutists aren't being realistic, largely for the reasons mentioned by 'defrost in response to you.
(NY Times lead economics writer Binyamin Appelbaum got it right in his book The Economists' Hour when he said, of Milton Friedman, that Friedman celebrated drivers but took roads for granted.)