Yes, getting rid of Saddam Hussein would have been a mitzvah--if we had not replaced him with a chaotic mess that was, for half a decade at least, significantly worse than being ruled by Saddam Hussein.
Certainly the national security of the United States has been harmed by the adventure. Iran is no longer contained by Iraq. And there are an awful lot more people in the world who have very good reason to hate America.(1)
1Why were We in Iraq ? - Brad De Long