The voluntary exchange of goods and services–free markets–does not stand on its own. In its fullest form, is is supported by a legal/political/cultural system. That system, among other things, includes a government and law that protects people from threats of violence from within and without, and promotes a peaceful, predictable means of settling disputes. But because government is given power that no other institution has, it also needs to be limited, so that it does not consume commerce or culture.
America’s founding fathers laid out the Bill of Rights as one element of their attempt to create a necessary government that was necessarily limited. But words in a document are not enough; the people must want and demand that the ideas of the document are respected, both by the citizenry and officials in government.
The answer to the old question, “who guards the guardians” is “we the people.”