Go for reading Jeremy Scahill’s book. I think it’s a great book, and Scahill does important research, and you should trust yourself to decide on your own terms what is and isn’t within the appropriate realms of bias. Scahill isn’t pretending not to have any opinions in his book, and I think he rightly makes it very clear what his arguments are. I would also recommend P.W. Singer’s book Corporate Warriors: The Rise of the Privatized Military Industry, which provides a look at a broad range of private military contractors in historical context.
A quick note on some of the phrasing involved in talking about this topic: It’s important to remember the division between the idea of “mercenary” and a military contractor. Mercenary is a narrow term that I find often demonizes the actual people on the ground and ignores the role of corporate decisionmaking and government oversight practices (which I consider the root problem of the current system of military contracting). That kind of phrasing also erases the fact that the majority of contracting personnel are not hired gun, trigger-happy Blackwater Xe Services Academi jocks, but people performing a variety of military support services (including laundry and electrical repair work) who are often exploited or put in peril by the companies for whom they work. It’s important to make the sharp divisions about what kinds of people we criticize. (Scahill’s book, by the way, provides us with some excellent examples of who exactly ought to be receiving our ire… *coughErikPrincecough*)