I'm just going to quote Jim Henley a bit:
Deborah Hastings of Associated Press explains what happens to people who blow the whistle on corruption in Iraqi contracting: very bad things. One man was detained for 97 days and subjected to “fear up” interrogation. One woman was demoted and ostracized after a blameless 20-year civilian career with the Pentagon. A KBR contractor who blew the whistle on invoice-padding and diversion of resources was kept under guard until she could be ejected from Iraq. The federal government, which has happily joined Federal False Claims act suits for Medicare/Medicaid and domestic contracting fraud, has declined to sign onto even a single lawsuit against contractors in Iraq.
Financial improprieties aside, I would further note that insofar as the rationale for our continued presence in Iraq is humanitarian, unleashing on the country a body of thousands of mercenaries who are subject to neither Iraqi nor American law seems like an odd way of going about that.