Well, thanks to @besttrousers for dropping the Iraq WMD grenade in my lap - you shall pay, Matt - but one thing to remember is that Saddam could have screwed over Bush and Blair by complying with UN demands at the last minute. In fact, U.S. was worried he'd do that. /1

Saddam's own generals later were debriefed and said stuff like "Well, my unit didn't have them, but the units near me did." When you're so good at this your own generals think they exist, you can imagine that foreign intel agencies aren't betting on the under. /2

No major intel agency anywhere dissented from the basic view that Iraq was hiding WMD. Weapons inspectors wanted more time to prove a negative, that Iraq *didn't* have them. Duelfer later found none, but intent to preserve the WMD programs for quick restart. /3

You can argue that invading Iraq was a bad idea, badly executed, or badly premised on WMD as the major reason. But "experts were stupid and everyone knew there was no WMD" is just 20-years-later retconning for a war that went bad for a lot of reasons.
/4x