Mercenary Companies

This recent news about Blackwater U.S.A has led me to think about "private security firms." Are they neccessary? Are they even somthing that should exist? Should they work with or seperately from a nations military? In answer I do not thing that they should be neccessary. A nation should have the ability to fend for itself militarily. However there are many nations that do not have strong military and are unable to fend for themselves. In the case of these nations I think military contractors can and should be used. Large states who are economically able to fully support their own forces should do so, for the simple reason that then if somthing goes wrong it is far easier to decide who made the mistake and what they did wrong. In connetion to that if private firms are used they should not be used to maintain supply chains and transportation. I say this not because I believe that they are unreliable but because supplies are absolutely neccessary to every military and should be soley controlled by that military. If a military is not in control of its own supplies there is far greater chance for error simply because those transporting it are less likely to be totally devoted to getting the supplies where they need to be. Private contractors are there voluntarily and can leave after their contract runs out they get their supplies seperately from the military and there for have no need to get supplies to a destination except to get paid, and many people prefer life over money. Private security firms are but should not be a neccessary part of the U.S. military, private firms while useful are in war for a profit and not to win.