Rumsfeld personally advanced the de-baathification directive - the lynchpin of the clusterfuckery - all on his own, and he certainly would have known to expect the 'unexpected' results to be similar to de-nazification. This was absolutely his choice. Another point you have (unintentionally?) brought up is the dignified resignation option. While it is often a naive, self-serving gesture, we can reasonably imagine that the Defense Secretary publicly resigning over opposition to a war during the public consideration of that war, might have had some effect on whether that war was started. I want to like him too, with his grandfatherly demeanor and genuine funnyness ("My god, were there so many vases?!") but, come on.