US suspends all land travel by US diplomats and other civilian officials in Iraq over Blackwater incident.

A semi-rhetorical question: why do we need Blackwater, a 'private security' firm, to provide security for US officials in Iraq when we have the US Army and US Marine Corps? Not to mention the various security agencies connected to the State Department and the paramilitary arms of our intelligence services?

I say it's a rhetorical question because I know most of the answers experts in the field would give. But none of them are very good answers. And many are very, very bad.