I think of the Iraq war as more "a waste of money" than something causing "massive numbers of people dead." The succession after Saddam was not something that was ever going to go well, which is what what actually happened should be compared to.

It could have gone a lot better than it did. After the US Gov deposed Saddam, they disbanded the Iraqi army. The Iraqi army was composed of evil, angry people with their own hidden arsenals - the sort of people we really, really don't want to have out of work and stirring up trouble. If we had given them all busywork desk jobs instead, at least for little while, I think that most of the violence would have been averted.