Legitimacy of PMCs in Public Discourse

[AmericanPride]

I'm doing a research project on the development of the legitimacy of PMCs in public discourse (specifically American). Despite a history of suspicion and distrust, as well as international law which condemns the use of "mercenaries" (however defined), PMCs have not only gained access to political ears but some might suggest that they have become essential to modern warfighting. Some questions I will be asking and (hopefully) answering:

Are PMCs considered any more or less legitimate now than anytime previously (probably with a focus on the American Revolution, and perhaps the Italian Wars, but suggestions for any other conflict is welcome). If there is difference, what public/ideological/legal norms have changed and why?

What present political conditions enable the use of PMCs? Specifically, what factor(s) compels a state to forgo its monopolistic right to violence? Are these factors related to the prominence of state-sponsored terrorist organizations? (Essentially, are PMCs and state-sponsored terrorists, legal questions aside, two peas from the same pod?)

What is the long-term impact of security privatization on national and military strategy? (Everyone has an opinion on that question )

I have a handful of sources with which to start -- if anyone has any good reads to suggest, they are welcome.