I'm pretty certain that the Bush administration was convinced that Saddam had WMDs. I'm also pretty certain that it was because we gave/sold them to him for his fights with Iran, before the Kuwait invasion.

Now, after we invaded in '03 and couldn't find the WMDs they started lying. Absolutely. But the basis for the war was incompetence.

Russia, France, and Germany seem to have much better intel, but we don't like listening to them. This seems to cross administration lines so it's not quite clear what the problem is (although that doesn't prevent a lot of speculation).