Mark, I fully agree with the point of your post. The road to peace for Iraq -- thru partition or another path -- will not be easy. Hence I said "fragmenting" and "developing." Nobody can tell how it will end.

My two articles on this topic (March 13 & Sept 27) analyze the same potholes as those you list:
http://www.defense-and-society.org/fcs/fabius_insurgency_ended.htm
http://www.defense-and-society.org/fabius/long_war_IV.htm

There are complex dynamics at work, beyond the scope of a post (hence the articles). Here is a summary of some relevant themes I (and others) have written about for the past year:

1. The mutual slaughter to date, and potential for much more -- perhaps spreading through the region -- provides powerful incentives for everyone involved to pull things together.

2. The development of local ruling elites provides a mechanism for this to happen. Ethnic cleansing makes it possible.

3. Peace is a relative state, esp in Iraq. There could be long-term border wars amongst the new Iraq mini-states, and between them and their neighbors. This is the most common scenario, historically.

4. The oil revenue is both a cause of tension and a solution. Money can be divided. Wars over ideology and religion are more difficult to settle.

5. The US is more of a passenger in Iraq than a driver.

6. Public opinion polls express people’s dreams and aspirations. For example, polls in American show broad support for both lower taxes and more public services of improved quality. These yearnings are a factor, but seldom a decisive one.