Re: If your not on the list, you're not getting in
Bottom line though is that US justification of attacking Iraq (that US had proof hat Iraq had WMDs) was patently false.
No it wasn't. We knew that Iraq still had WMDs in 1998 when the weapons inspectors finally got kicked out. Or at least, "knew beyond reasonable doubt". Iraq were still obstructing the team's attempts to destroy what was known about (let alone if Saddam had more that had avoided detection so far), to the extent of throwing the inspectors out.
So it was perfectly reasonable to act on that knowledge.
As you say, Iraq wasn't a threat to anyone but its own population in 2003. But it still had a vast army, a nice oil industry and a whole bunch of people who knew how to make chemical weapons. Plus it had a reasonably advanced missile program, as they'd been modifying and upgrading their own SCUDS for years - though I don't know if they were up to actually building their own engines.
So it could have made itself a threat again reasonably quickly. As I recall sanctions were up for renewal at the UN in 2003 and were expected not to pass. Even the French were talking about opposing them - though I suspect they'd have let the Russians take the heat for actually vetoing. Not coincidentally Iraq owed France and Russia billions for all the military kit they'd sold them, and also needed lots of spares and replacements.
Remember that the RAF and US Airforce were regularly shot at by the Iraqis, patrolling the no-fly zones to stop Iraq attacking the Kurds and continuing with the genocide against the Marsh Arabs. It's not like this was a stable situation that the evil US and UK were stirring up.
Who was to know that Saddam wouldn't immediately arm-up again and invade Kuwait and Saudi? There was nothing to stop him at the Saudi border in 1990 - and he could have made retaking Kuwait a lot harder if he'd continued over that border and destroyed places like King Khaled Military City. The logistics of desert warfare are a complete bastard. Not to mention the Saudi and Kuwaiti oil wells. And those are a global strategic interest. It's why we went to war in 1991 after all.