The problem is that some, such as the JCS, advocate the era of manned fighter could be over. If the force replaces manned aircraft on a one for one ratio, which is the plan, then they will fail just from reliability faster than man aircraft. This will increase, not decrease, budgets which is one of the driving rationales for the use of UAS.

These things fail at greater rates than manned aircraft in the current low air threat conflict. When intentionally targeted by a peer or near peer nation, they will fall from the sky like rain. The US will lose air superiority because we would rather invest in UAS than advanced fighters
http://www.cnn.com/2008/WORLD/europe/04/22/georgia.russia/index.html http://www.strategypage.com/dls/articles/Predators-Falling-From-The-Sky-Everywhere-9-21-2009.asp