Victor, you’re right that the administration over-invested in the WMD rationale and that this caused real post-liberation problems and provided an easy option for those who wanted to discredit the Iraq mission. You’re also correct that there were plenty of other reasons for toppling Saddam.
The trouble was most of the others – his attempted assassination of Bush pere, etc – meant absolutely nothing to the “international community.” WMD was the easiest sell to the rest of the world, and even then it didn’t sell that easily. I remember a member of the Blair cabinet, the late Lord Williams, the Leader of the House of Lords and a former Attorney-General, telling me that the Prime Minister had been advised by his lawyers that if he expressed support for regime change it would risk having the war ruled “illegal.” In an increasingly legalistic conflict environment, the narrow rationale of WMD was all that was available for Her Majesty’s Government to sign onto.
There’s an obvious lesson here which the much maligned Secretary Rumsfeld understood. Even when you go in with real allies who do real fighting (which most of the Nato “soldiers” in Afghanistan won’t do), you dilute your own national interests – sometimes, at least in domestic political terms, catastrophically.