Yet the use of contractors is not a free lunch.

Compared with the military, contractors are not subject to direct scrutiny by Congress and they are not covered by international law with the same clarity. Excessive use of private contractors erodes checks and balances, and it substitutes market transactions, controlled by the executive branch, for traditional political mechanisms of accountability. When it comes to Iraq, we’ve yet to see the evidence of a large practical gain in return; instead, use of contractors may have helped to make an ill-advised venture possible.

When private contractors are combined with government troops, the contractors usually can’t do much better than the setting in which they are asked to perform.

When things are going well and the “good guys” are in control, the flexibility and experience of military contractors can make things go even better. But when the environment is hostile and events are spiraling out of control, the incentives of private contractors may lead to many mistakes.

Note that a serious issue for Blackwater — the allegations about needless deaths of innocent civilians — has also been an issue for United States government forces from the beginning of the conflict.

Most of all, contractors are appealing when a victory is possible in relatively quick order. The potential accountability problems won’t linger for long; conversely, few contractors will look good when a conflict runs on for years.

Currently, the chances of establishing a stable Iraqi government appear quite low. In other words, there is little upside, and an unstated goal of American policy may be simply to limit the damage. If so, we should be cutting back on private contractors, as the critics are suggesting, because there is no desirable end in sight. Of course, those same reasons suggest troop cutbacks as well.

In the next conflict, however, the temptation to use contractors may again be strong. What if private contractors offer a real chance of making a positive difference? For instance, it was the private firm SITE Intelligence Group that obtained the first American copy of what is believed to be the latest video from Osama bin Laden, although it seems that government leaks have since damaged the trail of intelligence.

Private contractors may not respect virtue for its own sake, but like most businesses, they will respect the wishes of their most powerful customers, in this case governments. What is wrong with Blackwater may, most of all, mirror what is wrong with Uncle Sam.