What Saen said.
Also, the whole moral equation of “if I try to kill you, you are justified in trying to kill me” makes no sense in a vacuum.
If you are sitting at your PC posting to the SDMB, that’s one thing. If you are trying to rape and murder a child, not only am I entirely justified in killing you, you have no moral right to try to kill me in return.
Saddam Hussein and George Bush are simply not equivalent moral agents. It takes a pretty rabid anti-Bush partisan to argue that he deserves to die. People who believe that Saddam Hussein achieving room temperature would be a net benefit to the world are pretty common.
Legally, I believe the prohibition against assassinating a foreign leader comes from a Presidental order, not yet rescinded. So to specifically target Saddam would be illegal. Morally, I think you could justify it, although it might be a stretch, based on the principles of a just war.
Practically, it’s a slam dunk, and “a consummation devoutly to be wished”.