The real question is, who's next? There are any number of countries that pose as big a threat, if not a bigger threat to our future national security. The whole Axis of Evil thing.
North Korea, for example, already has weapons of mass destruction and serious domestic issues creating instability. Hey, didn't they once invade a neighbor, kidnap foreign nationals, kill American servicemen regularly in small quantities since the treaty, capture an American naval vessel, attack South Korean naval forces on a regular basis, attempt to infiltrate action groups using tunnels and mini-submarines, conduct aggressive and intimidating missile tests, disregard international treaties, etc.?
PRC, well, what's going to happen with Taiwan in the next decade? China can already incinerate millions of Americans at the push of a button.
Iran? They could be coming around though, somewhat, if the moderates don't get destabilized.
Pakistan, there is already an Islamic bomb and the potential for it to get in the wrong hands rather easily, given a successful overthrow. In fact, there is a strong Taliban 2 atmosphere in some areas.
Saudi Arabia? More of an international terrorist threat than Iraq, at least where 9-11 was concerned.
So, if this is an honest moral exercise, as opposed to some alternative motivation related to sweet Iraqi crude or a personal grudge, than we must continue to act until all these equal or greater threats are eliminated.
Charon