Somehow I thinkwe're really not wanted:
http://www.washingtonpost.com/wp-dyn/content/article/2007/08/06/AR2007080601401.html
http://www.indymedia.org.uk/en/2007/08/377824.html and they can't use the excuse that Iran or "al-CIA-duh" will take over.

Seriously, the comments about the "battle for control of the oil"-surely its "their" oil, and with no foreign troops, the militias would have have no excuse to oppress worker's rights. This may lead to more equal distribution of wealth, or at least stop oil profits leaving the country directly or indirectly in "reconstruction".

Anyway re. chaotic or precaric situations: if everyone in a specific region was in this position, surely everyone would work together to get everyone out of said situation (or at least would stop shooting at each other), even if each individual has only selfish or egoistic reasons for doing so, so surely their are always some (foreign troops if no-one else) who benefit from a chao-precaric situation.

The real reason for stationing British troops in Southern Iraq is probably the same reason "Azabush" Senior allowed the genocide of the Marsh Arabs and the Shias of the South at the end of the first Gulf War: doing so (or not doing so today) would probably lead to greater autonomy by the Shias, and thus greater control of the oil reserves.