... and I disagree. It only became predictable when we left Iraq for political gain, not giving the popularly elected government sufficient time to establish the infrastructure (both military and economic) necessary to sustain freedom.
Fight it out indefinitely? Hardly ... the military could - if allowed - go in and subdue the whole country in a matter of months. But, the methodology, and the result, would be socially unacceptable. It would require the complete subjugation of Iraq - set up a US military government for a finite period of time, and THEN go about rebuilding the country, politically, socially, and economically.
The reason it didn't happen the first time was because of our unwillingness to fight to win - everybody wanted to be a nice guy, buy their love, if you will. It just doesn't work -- never has, and never will.
When we look at your options ...
1) "do we let them fight it out among themselves" - it depends on what the perceived goal should be. Let's keep in mind that we have two different factions - neither of which represent the will of the Iraqi people - who are merely engaged in a power struggle to see who should be next to rape and pillage the land and people of Iraq. It is nonsensical to think that the extremists won't prevail - they are, after all, willing to expend all in order to win. There's nothing more difficult than fighting a zealot - they don't know when they're beaten, therefore, they are never beaten.
If our goal is to not be involved, then we should just let them fight it out - knowing that, sometime in our children's time, we will be forced to fight whoever wins.
2) 'send in air support' - Again, the only way we can do that is if the current government agrees to become all-inclusive. We can use our air support to force a stalemate (which is a viable and simple effort), but can't be perceived to be supporting one side of the other.
3) 'arms to the Iraqi government' - Totally unacceptable. It isn't our job to prop up a corrupt or ineffective government that doesn't represent all the Iraqis.
As for your assumption that the right answer was to 'have stayed out of Iraq' - I think history will prove you wrong.
