Assassinating Saddam Hussein would have accomplished nothing in terms of improving the lot of the people of Iraq, or of increasing security in the region as a whole. As like Assad's succession in Syria, Saddam would have been replaced by one, or other of his sons, who potentially were a damn sight worse than their father.

Saddam Hussein could only ever been killed in the manner he actually was.

Saddam Hussein had to be removed from power - which he was

Put on trial in an Iraqi Court to answer the charges against him - which he was

Executed in accordance with Iraqi Law - which he was.