You know how it works, if we had not gone into Iraq this fighting would not have happened, ergo, we are to blame for the fighting. It's understandabe why they say this because it's lazy and very easy thinking that is commonplace, particularly on the Left which is defined by its Hegelian tendencies to see the world through a master/slave, oppresser/oppressed type prism.
However, what should really be remembered is this. Saddam Hussein was a Sunni, and the Shias were considered scum of the earth and subjected to all manner of horrors under his regime. To thus play the comparison game and effectively say that if more die now than died under Saddam it would have been better to have done nothing simply results in two things. Firstly it is little more than 20/20 hindsight, but second, and much worse, it places the value of human life as little more than a statistic whilst masquerading itself as a moral position.
Frankly this is what sickens me most about the anti-war Left. They claim to care and cherish human life, and yet they will simultaneously be willing to sit on their hands and reduce that human life they care so much about down to a numbers game. Just look at what some of the idiots bang on about if you don't believe me. They scream about a million deaths in the war (a bollocks figure incidentally) and effectively postulate that because less died under Saddam it was 'better' under his dictatorship. What that really shows is that they don't care about human life at all, what they care about is their own moral self-righteousness.