That's hindsight, but sure, we can go through it again, if you'd like.
1. Defiance, clear defiance of 17 UN resolutions
2. Firing on our aircraft in the no fly in violation of ceasefire agreement
3. Open praise of 9/11, something no other country did.
4. Links to terror, at minimum suport for Palestinian suicide bombers
5. Failure to account for tons, literally tons of WMD materials as required
Now, let's put it in context, as I did earlier:
You're the President. The nation has just experienced the worst terror attack in history. You realize that we're at war with islamo-facists that want to destroy the Western World as we know it.
Now here's Saddam. He has done all of the above. Every major intel agency on the planet tells you that Saddam has WMD and is currently producing bio and chem weapons, and has possibly restarted his nuke program. Tenet tells you that the case for Saddam having WMD stockpiles is a "slam dunk" Saddam also tortures and gases his own people. He's a brutal dictator in the ME that hates the US. So you ask yourself: Are you willing to chance that this guy is NOT going to arm a terrorist group with one of these weapons?
Now, you go to the UN. They pass another res. after years of failed ones, this one giving Saddam one last chance, lest he face "serious consequences." Now, the UN already tried sanctions. The US tried limited military strikes in 1998. The result? Saddam continued to refuse to comply. He didn't give full access to the inspectors as he was required to do.
Look at the list. Look at the context. Are you telling me there was no provocation? Many wars have started without one nation directly provoking another with military action. The whole idea of pre-emption was to not wait and see. What other choice was there? We had tried everything else and were no longer willing to take a chance on this guy. Prior to 9/11, it was a different situation. But that event changed the way we percieved threats to our national security, as it should have, I guess I can see you disagreeing with the call, but to say there was no provocation is dubious.