Doudou, I agree that the decisions are made primarily for expediency and national or self-interests and that every country dresses them up in their own spin. This has always been a fact of international politics and will continue to be the case.
However, we know why France, Russia and Germany are taking the line that they are in this case, we can suppose to know why the US is taking it's line (although their reasons are slightly clouded by 9/11 and failing to get OBL as well as the economic and infuence aspects), but the question still remains unaswered for the UK. Tony 'Spin' BLiar has always tended to go with public opinion or direct public opinion so that he could be seen to go along with it. At the very least, he has used misdirection to keep the public away from decisions that they wouldn't like. This time, he is jeopordising his political future. I thought that he wanted to be President of Europe downstream, but his current stance seems to have killed that ambition for good - the same for a cushy NATO or UN position. The UK doesn't stand to benefit economically from a war in the same way that France and Russia will from a continued uneasy psuedo-peace. So why his stance? Moral grounds? I doubt it I'm afraid (too cynical these days).
Maybe to re-establish the 'special relationship' with the US that the UK has always thought it had. Admittedly the Americans haven't been aware of such a 'special' status and, indeed, considered Germany to be its favoured European ally until very recently (within the last year).