Because according to LAM laissez faire capitalism(libertarian economic policy) is a fantasy.
in regards to the markets ever being totally free from regulation, laws, government intervention, etc. they are what shape the markets it is a legal infrastructure that separates ownership from labor, creating an inherent "owner-friendly" marketplace which is based on property rights excluding communal rights.
capitalism has a natural advantage over labor, once you add in things and changes like fiat money that constantly devluaes it'self over time, how extreme inequality of income and wealth changes people (because money isn't value neutral), lobbying/special interest groups, one-way "free trade" agreements, regressive tax policy, anti-labor union movements and or "right to work for less wage" laws, de-industrialization, a capital class that is legally allowed to seek rents, financialization of economy's and a legally corrupted representative democracy it all swings in favor of the supply-side of the equation. and what do you end up with? the complete subjugation of labor by capital, and that is the US economy of today.
so yes the "regulated" version of laissez-faire capitalism brought the US the era of the robber-barons of the late 1800's and the modern day versions of them today like the Koch brothers, Apple, Wall Street, etc.
anyone that thinks that laissez-faire capitalism benefits society as a whole hasn't bothered to learn global economic history because empirical data shows the exact opposite. neo-liberal policy is nothing more than the "regulated" version of it. those that are for the "privatization" of infrastructure never even bothered to learn that initially public corporations were created in the first place to aid in capital accumulation. One of the more important reasons for their creation was the need to reduce costs to the private sector by means of government provision of infrastructure.
the only sustainable economy's combine the two (public and private sector ownership) in some manner, only the un-educated radicals (or modern day robber-baron's) spout the rhetoric of it having to be "one or the other", capitalism or socialism, etc.