If you're going to commit to going to war with an adversary, you must go for the kill. Doing anything less, virtually guarantees you'll face him again in the future.
That is warfare 101.
If Bush The Elder had taken Saddam's head on the first go-round, there might never have been a Gulf War II.
His nimrod son took Saddam's head a decade later. It led to the quagmire that our adult leaders knew would happen & had the wisdom to avoid.