Well, in fact, we can compare the situation with vietnam at least in a qualitative perspective. And I'm sure nobody in the USA wants to wait ten years and 50 000 dead people...
Problem is now : How can the USA leave the country without being responsible of a possible (mostly predictable) civil war and maybe genocides (kurds, sunnites or shiites).
All exterior interventions from western countries at least (but not only western) ended in blood. Just because the war is a strong destabilisation factor.