There's probably little legal clout to the Iraqi government's vow Monday to expel the security firm that protects American diplomats. But that should not diminish the importance of the incident the day before, in which eight Iraqi civilians were allegedly killed by diplomatic guards, or the ongoing controversy about the conduct of the U.S. Embassy's security force. In addition to the personal tragedy for those cut down while passing through a busy Baghdad square, this was a setback for the very interests American diplomats are trying to promote, and it is largely of America's own making.

That's because the dispute isn't really about whether the gunners for Blackwater USA were at fault for the deaths that occurred when a convoy of SUVs reportedly returned fire from unidentified gunmen in Nusoor Square. First accounts are often wrong and the full story may never be told. The question is whether anything would happen to the guards even if they did kill innocent people. Through multiple decrees by past American administrators in Iraq, later imposed on the Iraqi government, contractors are largely immune from prosecution for the force they use here against Iraqis. There are some 20,000 to 30,000 private security contractors here now, presumably about the same as their presence over the past three years, and none has been prosecuted for the use of excessive force against local residents.

Iraqis know this and point it out constantly with stories of deaths involving contractors. A notorious one in the Green Zone was the allegedly unprovoked killing of a guard for an Iraqi vice president by a Blackwater employee on Christmas Eve. (U.S. officials acknowledged a killing occurred and promised to investigate.) Iraqi politicians cry out for changes in the Iraqi law to end what they see as the impunity of the contractors and note the contradiction it poses amid American efforts to promote the rule of law by the Iraqi government. U.S. soldiers who commit crimes here can be punished and have been jailed under military codes, but those don't apply to contractors. They often just get a flight out of the country when they get in trouble.