What will happen if Iraq never uses any of the banned weapons, and it's found out that it's because they don't have any? Then what? "ooops!"?
I seriously doubt that will be the case but (hypothetically speaking) if it is then I would be absolutely livid at the U.S. government, particularly because of the Powell tapes presented to the UN. If Saddam has no WMDs then that means those audio intercepts were blatant forgeries.
Now I expect my government to use small-to-moderate (depending on the size of the crisis at hand) lies, as all countries do, to further the national interest, but perpetrating a gigantic hoax like that is irresponsible and absolutely unacceptable relative to the threat Iraq poses, because such a fabrication (i) is so easily exposed, critically damaging U.S. credibility in the process (ii) stirs up anti-American sentiment around the world and (iii) costs lives for no reason whatsoever. Assuming Bush knew about such a trick impeachment would obviously be appropriate at that point.
But like I said, I really doubt that will be the case. Occam's Razor, right? Saddam has a history of illegally developing WMDs and concealing them from the UN, so his culpability seems to be *infinitely* more likely than some vast government conspiracy. The real question is: If the U.S. does find WMDs will the rest of the world believe it or will they remain stubbornly committed to the conspiracy theory and label the finds as American plants?
The way it seems right now (assuming that they do have banned weapons) is that:
1. they don't use those weapons and face a certain defeat
2. They use those weapons and get a fighting chance against the coalition.
Those two premises are false. WMDs (with the exception of a significant nuclear stockpile, not applicable in this situation) would not grant Saddam "a fighting chance against the coalition"...they are essentially worthless when it comes to influencing the course of the war as a whole.
WMDs would help a little, but even then their effects are limited against troops with high quality NBC protective equipment such as that employed by U.S. and British forces. If the Iraqis used them they would probably end up killing more of their own troops than the enemy. The main benefit of WMDs would be to make individual coalition soldiers less efficient by forcing them into cumbersome gear, which is a real nuisance but not enough to genuinely shift the balance of power. To have any effect on the outcome of the war WMDs would have to be used on civilians in an attempt to indirectly influence the war by affecting public opinion. AFAICT there are two options to choose from there. Saddam could use WMDs...
(i) ...on the Iraqi people. This would have at least three benefits. First, it would instill more fear to help keep the Iraqis in line and fighting against the invaders, but thus far the Fedayeen seems to be handling this task quite well on its own. Second, Saddam would undoubtedly blame the deaths on the coalition, filming dozens of bodies strewn about the streets of a town and beaming the images across the Arab world as (probably highly effective) propaganda. And third, driving up the total body count by any means available would be handy as a last ditch effort to make the war *politically* disastrous beyond recovery for the coalition governments.
(ii) ...on the American and/or British people. Here his reasons would be two-fold, I think. First, simply to get a tiny bit of revenge against his enemy by attacking people that are far more vulnerable to the effects of WMDs than their uniformed counterparts. Second, to frighten the American/British public into backing off its government's stance, though it seems more likely that such an attack would only build hatred for Saddam and redouble support for the war.
No possible WMD strike would have any significant effect on the war being fought on the ground. Their use would be more geared towards a psychological or political victory. The problem with such a goal is that the stigma attached to WMD use would *far* outweigh any benefits, particularly because Saddam's current strategy is to play the role of the poor, persecuted Innocent in an attempt to curry favor with the international community and possibly provoke an outside intervention. So in that respect he has nothing to gain from using WMDs and everything to lose.
Saddam is not stupid. He knows that his forces cannot directly oppose the might of the U.S. military, even with WMDs. Since he is banking everything on a political resolution to the conflict, justifying the invasion in the eyes of many viewers around the world by using WMDs would be counterproductive. If Saddam does use them, I think it will be a sure sign that he has given up on his political efforts, and in doing so conceded the war. At that point he would simply be firing indiscriminately, trying to take as many of the enemy as possible down with him regardless of the political backlash (which of course won't matter to him when he's dead).