I just skimmed over this so I apologize if I missed something.

What you are describing sounds more like Juris Naturalism (which I tend to agree with in many ways) or Libertarianism than Anarchism (the absence of government) to me. In a common law system based on the principles of 1) Do everything you agree to do and, 2) do not encroach on others and their property, what MtGox did would be a violation of contract law and they would owe restitution (not that they could pay it) and perhaps face other penalties. In an anarchist system, MtGox could barricade the door and fight back the angry mobs that represent the only form of "justice" with guns (assuming that anarchy is possible, which it isn't, because where no government exists, someone will create one).

In the current system, which is the other extreme, even the most honest exchange is forced to comply with thousands of unreasonable and costly regulations that do more harm than good and don't actually protect customers. The average cost per capita of regulations is something around $10,000+ per year in the US.