Originally to provide a justice and defense system, both of which are generally regarded as places where market forces would not provide a solution that would a

Originally to provide a justice and defense system, both of which are generally regarded as places where market forces would not provide a solution that would adequate protect the rights not ceded by the people to the gov't. Of course, after retaining this right the gov't expanded it for all manner of other purposes. You also have to remember that in most non-US countries rights flow from the crown/gov't to the people, not from the people to the gov't, so the legal justification would be much different and along the lines of "because we didn't cede that to the people"