You never seem to get it from the mainstream news and "entertainment" sources, but there was a rationale behind our ."humanitarian intervention" in Iraq, set out nicely from this piece from Prager University in about 5 minutes:
Me, well, I'd just say that Saddam never complied with the terms of surrender following Desert Storm and that was reason enough. Peace treaties don't mean a thing unless you enforce them.
As for the U.S. support of Saddam against Iran - well, which side would you have supported? Life is full of tough choices.