Interesting post and no real answer, but the question should not be based in emotion as most of this thread is. The one thing we should ask ourselves is;
'Do you believe in a nation's right to sovereignty and self rule'?
If you do then a unilateral invasion of Iraq cannot be argued for. The UN though a deeply flawed decision making body must initiate action.
It's takes one exception to qualify the norm, unilateral action is a very dangerous exception indeed.
BTW I'm pro yank and very anti Saddam but the US must go through the UN.