Robb has a good blog post on why we will, not should, but will stay in Iraq and Afghanistan for some time to come.
He lists three core reasons, the last of which intrigues me especially:
1. Superior Marketing
2. The elasticity of the conflict (i.e. the notion of a war on terror)
3. privatization of the conflict.
I don't know to what extent the last one actually explains the current acceptance or reluctance to alter the status quo. Clearly the lives lost have been far too many (one being too many). That said, in terms of historical norms of armed combat, Iraq casualties are strikingly few. That said Blackwater and security firms of the like do lose men in combat (under contract) and this does not figure into public calculus.
hat tip: Ross Douthat