Iraq: Just one stop in the war on terror
Why WMD was never a key issue in the decision to invade Iraq
Those same people seem to forget that there were a lot of other low hanging fruit reasons to invade Iraq. One of the most obvious is, if he didn't have WMD, then Saddam was a fool to flout the UN resolutions and mess with the inspectors (let alone throwing them out of the country). And regularly shooting at our planes flying the no-fly zone sure didn't help either.
Ultimately though Iraq is just one battle in the war on terror. It's not about the oil. It's not about imperialism. It's about defeating the Islamo-fascists.
In World War II, the United States and Britain had to invade French North Africa in order to get at Rommel. Geographic location was the key.
Let's look at the Middle East from a fresh perspective:

There's Iraq. Right in the middle. It has a port right on the Persian Gulf. The 3 of the 4 most significant sources of Islamo fascist terrorism have borders with Iraq: Syria, Saudi Arabia, and Iran. Only Egypt is not on the border.
There are two basic ways to defeat Islamo Fascism: Try to conquer it and re-educate the people (the World War II method) or try to have a country of similar culture take a different path and become so successful that the native populations of the target countries begin to demand their governments change (The Cold War Method).
Now, before I get emails, Islamo Fascism should not be confused with the religion of Islam. Islamo Fascism is specifically an authoritarian movement by Islamic extremists that want to turn Islam into a form of government and views all those who do not conform with their views not just "infidels" but true enemies who must be exterminated. It is in their culture's failure that we have become their target. Our obvious success despite being infidels represents a threat to them, a threat they hope to wipe out through increasingly deadly attacks (September 11th was merely the culmination of nearly 10 years of attacks of increasing intensity on US interests).
Iraq was simply the best choice where to start. We live in a politically complex world and the US couldn't just invade Saudi Arabia or Iran. And Afghanistan (just east of Iran) is land locked which has made operations there a pain. But Iraq...well Iraq was a different story. First, I believe that the administration, just like previous administrations, truly believed Iraq had weapons of mass destruction. Secondly, Iraq was flagrantly supporting terrorists (mostly Palestinian terrorists). And lastly, there were a whole series of UN resolutions against Iraq that Iraq had flouted thus giving the United States the legal justification to commence military operations.
Now the hard part comes in. What do we do next? Do we build up troops in Iraq and use force (overt or covert) to topple the regimes of Syria, Egypt, Saudi Arabia and Iran? Or do we work to build up Iraq as an example for the rest of the region. Just as West Germany served as a stark reminder to Eastern Europe that there was another way, a better way, Iraq could serve as a beacon to those countries whose clerics and militants currently have a disproportional influence on the population.
Either way, the invasion of Iraq was not about oil. If Iraq had no oil and all the other conditions existed, I believe we would have gone in anyway. Just as we went in to save South Korea in the Korean War (but that was because of the fear of communism right? Sure, and this was because of the fear of Islamo fascism, this project in Iraq is far too expensive to justify if oil was the goal -- oil sometimes costs less per gallon pre tax than water in some places).
As for weapons of mass destruction, I suspect we'll find them eventually. But their existence is largely irrelevant to whether we should have invaded Iraq or not. At most, it's a minor political pain for the administration. But since both parties believed Iraq had WMD for years, it's not a significant issue. What is a significant issue is rebuilding Iraq and making it a base for our operations. Better to fight the war of hearts, minds, and bodies over there than in New York.