You (and Rob) are obviously correct in that there was a background to this current situation that would have probably wound up the same, I acknowledge that. But we did accelerate the process, and we did a horrible job at stabilizing the country to boot.
Put it this way: say there is a sandcastle on the beach. Eventually it's going to be washed away by the waves. That doesn't make it anyone's right to go take dump on it even though its fate is sealed.
Even then, in this case who knows how the situation in Iraq would have turn out had the US not have invaded. Your scenario is the most likely one, but there were possibilities for some sort of popular revolution that would not end in this sort of civil war. While it makes sense to say that yeah, it would have wound up like this, we accelerated the issue to the worst possible conclusion, not anyone else.
Yeah, we've inherited this problem, and abandoning it right now in the long run won't help us one iota, because to the rest of the world we were the bad guys.
Of course not to the first point, and the second point you make shows why Israel has a vested interest in the fate Iraq. That was my point. They are going to be active in the future of Iraq, to say the least. Maybe not invade, but Mossad is good at what they do if you get what I mean.