Ok for the record the Iraq war was wrong it was not legal and caused much destruction. Many, many, Iraqis died unecessarily. Saying that we cannot blame the Americans for what is happening now, old scores are being settled and we can’t keep blaming that on the usual suspects that is simply an act of denial.
I’ve already made it quite clear that I am not defending the Americans so let’s move on with that.
Lets also use your example, now if the Americans were to burn down my house that would be their fault and would be to blame. If though once the house is on fire the neighbours were to take advantage of the situation and loot my property and take control of my possessions that would be their fault.
The Sunni and Shia rebels choose to bomb one another, because they don’t want to see the other in power. Saddam had kept the religious nuts under control but now they are free to do as they wish.
Your last point although said rather crudely is what i was alluding to the Americans tipped society upside down and left the place as a sectarian battleground now whose fault is that.
When you remove a working government/institution and let chaos take over then step out of the scene does not absolve you from the crime/sin you committed.