The only legal justification for the war was that Saddam had a stockpile of Weapons of Mass Destruction he was getting ready to unleash on the world duirectly or by proxy, and that he resolutions passed bybteh Security Council entitle member states to take immediate action to get rid of them.

Getting rid of Saddam was just a bonus, not the legal ground for the invasion.

At present it's looking as if that claim just wasn't true. If so it was either a lie or a serious failure of intelligence. And that matters.

Saying thta it's all right anyway because it got rid of a wicked dictator is a bit like saying that a lynch mob is ok because, on a particular occasion, it lynches a real crimninal.