Yes, there are a lot of bad people in the world. Yes, Saddam was one of them. There are others, too. When do we invade Saudi Arabia? Libya? The Sudan? Manila? Sri Lanka? Korea? China? Mexico? Canada? Terrorists have been "harbored" in all of the above places, and then some.
We'll never end radical religious extremism unless we kill all the religious extremists, not only Muslims, but Christians, Hindus, and Buddhists. Then, I guess we'll have to round up all those extremists of atheist persuasion, and kill them, too. How lond do you suppose that'll take? [/sarcasm]
In my opinion, since we'll never be able to kill them all, the next best thing is to be selective about who we kill. If a person or group attacks us, we should leave no stone unturned, until we root out that person or group, and kill them. Religious extremists of whatever stripe should be able to feel it in their bones... attack the United States, and you'll never find a hole deep enough to crawl into.
Our business shouldn't be "nation-building" (a concept abhorred by Bush in his Presidential debates). Our business should be finding those who attacked us, and removing them from the planet. My own thanks go out to any who serve in this conflict. My sorrow is that they've been used as tools to get the wrong job done.