Changing The Narrative

A reader asks a good question:

I need an explanation. The common argument for why we "cannot lose" in Iraq, is that it will result in a breeding ground for terrorists (specifically Al-Qaeda) in Iraq - much like Afghanistan was (is?).  But doesn't this assumption rely on the same misunderstanding that haunted Congressman Reyes, that there is a significant difference between Shiite and Sunni.  If we leave Iraq, I suspect the civil war would escalate. Who would win?  Almost certainly the Shiite majority.  Why would the Shiites then allow Sunni terrorists such as Al-Qaeda to set up shop there?  I don't see why they would.  So the result would seem to be a Shiite state and no large-scale Sunni terrorist activity (certinaly none focussed on the US).

I recognize the problems of a possible genocide against the Sunnis and of an Iranian puppet state.  But those problems are wholly different than the argument made by Bush and his supporters that leaving would result in an Al-Qaeda breeding ground.

Where am I wrong?