Your requirements are absurd - Every business will be subject to some sort of government regulation that could limit barrier to entry. That's why your conclusions are outlandish- Microsoft was literally deemed to violate antitrust law in federal court; there are plenty of obvious historical examples (United Fruit, Standard Oil, US Steel); Pharmaceutical companies consistently exhibit price gouging in medical monopolies, etc. Furthermore, oligarchical monopolies, like the telecoms, are not somehow exempt- they operate, lobby, coerce, and consolidate power together, despite being 3 separate companies. Utilities are generally natural monopolies, not government created- the major barrier is the huge costs on upfront infrastructure, which dwarf any regulatory costs. Most importantly though, you failed to grasp the fundamental concept, that a government granted monopoly is not somehow uncapitalistic: it's hypercapitalism, the end goal of the system itself.

The seems like a life imitates art/art imitates life question. It seems impossible for a completely unbiased government free from favored interests. Every sufficiently large corporation exerts influence or receives favors as a localized tax source or employer of voters.

Do you know why regulations in the US exist? Because of the robber barons of the gilded age.