A good question, and one that really deserves a better answer than I can deliver. I'm not a professional researcher or reporter. I'm a recruiter on leave who has Google. It's not a combination destined to survive peer review. That being said I think the crux of the "No WMDs have been found" camp is that, by the strict definition of the UN and the Iraqi Survey Group that searched for WMDs in Iraq, they have found none. Despite field units detecting the presence of blister and nerve agents in bunkers and depots across Iraq none of the field positives tested positive in the official lab.
I'm going to assume that it's well known that after the Gulf War Saddam decided he was going to have access to WMDs. But the inspection regime made it difficult to do so. France was probably not going to help build another Iraqi nuclear reactor, and it's freaking hard to make nuclear weapons. Especially if you don't want a mess of inspectors to find it. Biological weapons are easily hidden and very potent, but if discovered by the inspectors there is no recourse. You can't claim you were making anthrax for any reason but to use it as a weapon. It has no other use. Chemical weapons are a very different beast though.
The WMD claim made by the administration (I'm not an official source, running by memory here) is that Iraq had "stockpiles" of WMDs.
Saddam realized that the presence of nuclear or biological weapons would be a dead giveaway. There is no hiding of them. You can't build a clandestine nuclear reactor and claim it's not for blowing stuff up. You can't grow lab-quality biological agents and claim they're for anything but killing people. You can, though, create as many chemical weapons that you want, but claim they have another use.
A quick Google search on chemical weapons reveals some wicked sinister stuff. The sort of stuff that Bond villains would do. But it also reveals that, at the base of the pyramid, it's some easy stuff to do. A trip down the household cleaner aisle at Target and a 10th grade chemistry class are all you need to close down a building because of a chemical attack. They're easy to make and easy to disguise. The earliest chemical weapons were just industrial chemicals like chlorine and phosgene. In WWI the German's just took vats of chlorine, opened them, and let the wind do its thing. The French then loaded phosgene into artillery shells and fired them on the Germans. The lesson is that chemical weapons would be a perfect weapon for a clandestine WMD program.
It's a lesson that Iraq learned well. I remember there being several reports of American forces finding stockpiles of chemical weapons. 55 gallon drums of liquids causing positive results for blister and nerve agents. The contents of those drums? Pesticides. Agricultural pesticides. Now, why these pesticides were being stored in underground bunkers, with artillery shells and missiles, and military chemical protection equipment are beyond me. I'm sure there is an explanation of why those pesticides weren't being stored on... I don't know... a farm. But I never heard it. It seems that the ISG decided that if the container didn't say "Sarin" it wasn't a WMD. Even though everyone exposed to the container came down with the symptoms of Sarin. That the administration seems to have went along with this is... depressing (my opinion, not an official statement).
At their core pesticides use an organophosphate chemical to cause their pest-killing. Basically the OP goes about shutting down some bodily function. Ceasing nerve function, breathing, muscle control, whatever. As near as I can tell most chemical weapons are highly refined OP chemicals. So, having a massive stockpile of pesticides would be a really good way to have a less massive, but still sizable, stockpile of chemical weapons just waiting for refinement and delivery to an unsuspecting invading army or dissident village.
A cake is made of flour. There are a whole lot of other ingredients that go into the cake, for sure. But without the flour you're not even going to make something that even remotely resembles a cake. Flour is a very versatile material. It can become cookies, tortillas, pancakes, waffles, and a whole host of other delicious treats. Organophosphates are the flour of the chemical weapon world. There are a whole host of legitimate reasons for a country to have a stockpile of pesticides. When those pesticides are stored in a military bunker, with military equipment to handle them, and the only delivery system present is military in nature (mortar and artillery shells, and missiles) one should make the assumption that the chemicals are for a military use. That doesn't seem to have been the decision made by the ISG.
The ISG seems to have looked at a drum of pesticides and a crate of mortar rounds and said that the two are unrelated. Sure, they could be used together, but they aren't at this second so it's totally innocent. Sure, Saddam has a history of using rounds filled with chemical weapons against own his people, but he hasn't done it in a long time so stop bringing up old stuff. This is like saying a gun isn't a gun until the bullet has been loaded, or a knife isn't a knife while it's still in the sheathe. It's insane.
It's our own fault really. We didn't move fast enough to counter the "no WMD claim". It's taken hold and now accepted as fact. That President Bush joked about it during a speech doesn't help. Instead of saying "We'll find them in the next bunker" when the ISG results came back negative for a pure CW, we should have said "Well, why the hell did an innocent pesticide trigger the alarms, and why are they being stored by the Iraqi military with weapons capable of delivering it?" Oh well, worms are out of the can, horses out of the barn, Pandora has left that box.
I can't control things on a national scale, except when I'm playing Civilization 4. But the next time that the professional student comes by I'll have more to say to him. And that makes me happy.
Hope everyone enjoys their week. Sorry that this was such a poor post. I had a much grander thing in mind, but my plans never survive contact with reality. I'm off to conquer Sid Meier's world.