Iraq: WHY?

Amusing though it was to see William Shawcross billed as an "author and broadcaster on the Middle East", rather than just as "his father's son" or "the (yet unpublished) official biographer of the Queen Mother", this evening's BBC Parliament debate on Iraq left the main question unaddressed: why?

It can't have been because of WMDs, since no one making any decisions ever believed that there were any. Therefore, it can't have been because of Israel (which has nuclear weapons, anyway). Nor can it have been about oil, which Saddam Hussein was perfectly happy to sell to us.

And it certainly wasn't either about Islamist terrorism (against which Saddam was a bulwark), or about making life better for Iraqis (who were better off under Saddam), or about containing Iran (which has never been stronger, her enemies both to the west and to the east having been removed), nor about preventing an Islamist takeover (which, entirely predictably and indeed as widely predicted, has come to pass both in a Shi'ite form in the south and in a Wahhabi form in the centre).

So why did we ever go to war in Iraq? And why are we still there?