Do you really believe there was little or no justification?
The UN and the whole world agreed that Iraq had WMDs at the close of the Gulf war. The war ended with Iraq's promise to destroy them all. UN inspectors were evicted after a time and Iraq never produced evidence that it kept it's word.
What happened to the nerve gas? what happened to the Biologic and Nuclear material? Where's the proof they were destroyed? Saddam's word?
I don't believe we should have attacked them if there was no immediate threat since we had them contained but there certainly was justification.