There is a problem about lying over WMDs that is unique to Britain, and to Mr Blair. If the war was fought to advance democracy, and to overthrow a tyrant — and these would appear to have been Blair’s better motives — than it needed to be fought by practising democrats.
Part of democracy in general is that you don’t start wars, even just ones, without a democratic mandate. British democarcy, in particular, has a foundational principle that you don’t lie to parliament.
The accusation about WMDs is that Mr Blair’s parliamentary mandate for this war was obtained by deliberate, conscious fraud. That’s to say, he constructed a majority in favour of a war of self-defence against Iraq, or one to enforce the authority of the United Nations. There was no majority for a war to overthrow a repulsive dictator and govern his country in perpetuity.
Note that this is separate from the argument that says that Blair’s war to liberate the Iraqis was a bad or ignoble idea. It’s possible to approve of liberal imperialism in principle while believing that our practice of it is pretty disastrous. The point is that no one voted for the liberal imperialists’ war. Parliament voted for a different war, on the basis of lies.
The snag with this reasoning is that most of the Conservative party would probably have voted for anything the Daily Telegraph told them to do. I do know that. But it’s not a fact that will mollify the labour voters and MPs in whose hands Mr Blair’s future now must rest.