I'm OK will libertarians. They're quite entertaining, and provide some comic relief. I could have a beer with Gary Johnson, and maybe give him some pointers on Mid-East geography. The problem comes in when some start to take them seriously.
Johnson is an ideologue, with extreme and unfounded notions about the workings of the world. Johnson's fundamental error is in thinking that the federal government is the same type of entity as a business or private person. It is not, in significant ways. His nutty ideas for eliminating all personal and corporate taxes, while instituting a regressive VAT of 23%, would crash the US economy within months, and bring in a new great depression. Elimination of the IRS and the Fed would take away some of societies major tools for regulating society, a void that would be quickly filled by transnational corporations, and foreign governments. America would become the 21st century equivalent of China in the 19th, weak, divided, impoverished, and open to myriad foreign interests.
In actuality, you cannot have either personal liberty, or free markets, outside of a strong public regulatory environment. Johnson's psychedelic applications of economics may have muddled through in the small and (apparently) compliant state of New Mexico, but they would be disaster on the national scene.