If there have been 100,000 killed in Iraq since we arrived there, I can guaran-damn-tee you they weren’t all killed by Allied or American forces. The majority of innocent Iraqis were killed by the IEDs, car bombs, and devices placed in markets and other crowded sites in the country. It was the terrorists (I won’t call them insurgents, because so many of them were from outside Iraq, and were recruited to come into the country to fight the “Great Satan”) who targeted innocents as well as Allied and American military forces, and caused the deaths of the vast majority of the civilians killed in the past 10 years.
Obama's drone strikes have killed a lot of innocent bystanders, but no one is saying that Obama or his advisors should be tried for war crimes. It's possible that he has caused more deaths of innocent civilians than the US did in accidental killings in Iraq.
Given Saddam's record, if the US had not invaded, probably a larger number of Iraqis would have been killed at the hands of the regime in the last ten years than died by all the violence since the invasion. The left never brings that into the equation.
The biggest unknown is whether Saddam would have managed to develop atomic bombs--if he had the death toll surely would have been vastly higher than it has been since 3/19/2003.
Bush's false premisses were two--that there were large stockpiles of weapons of mass destruction in Iraq, and that the Iraqis were capable of forming and running a decent government if given a chance. The latter was just wishful thinking...like Woodrow Wilson thinking he could make the world safe for democracy.