One of my major formative influences was the Civil Rights Movement. One of the things I took out of it was that laws are sometimes unjust, and that you may have a moral justification, maybe even a moral obligation to break those laws. Perhaps the laws were promulgated by a minority, but perhaps they had majority support. In any case, you should not automatically say, "That is the law; you must obey."
Which is why I had such a cognitive dissonance when people who I'm sure would have felt proud to march with Martin Luther King, said, "You can't do anything unless the U.N. Security Council approves. It would be illegal."
(Actually, the article is only slightly about legalities. That's just my 2 cents.)
and sent this link. The "Humanitarian intervention" section basically articulates why i supported action in Iraq.