Opposing the Iraq War and opposing Blair's support for the Iraq War are not the same thing -
As Harold Wilson found out, there are economic consequences for disobeying the US. It would have been braver of Blair to stick two fingers up to the US, but probably not in the UK's economic interest and probably therefore not in Labour's electoral interest either.
I never believed Saddam had serious WMD capability. I don't think any politician believed it either (much as they now claim it). The big threat Saddam posed was in PetroDollars. Watch out Iran, N. Korea, Venezuela or anyone else who prices their oil in Euros.
I also never believed that this war was about democracy. The history of US and UK foreign policy doesn't bare this democracy theory out, no matter how much the Euston Manifesto-ers squeal that this is anti-American prejudice. Remember it was the US that overthrew a democratically elected secular government in Iraq and replaced it with Saddam. It is possible to be pro-US people, oppose the Iraq war, support Blair's decision to back Bush and yet still oppose Bush's foreign policy.
Of course the fact that the Iraq war was carried out for nothing more than stealing their oil, doesn't necessarily mean it will be bad for the Iraqi people in the long term. The omens aren't good though, as civil war takes hold. Perhaps the US will be bothered enough to try and buy the 26m Iraqis off with a decent standard of living, quite affordable with the amount of oil profits available (but then again perhaps they won't be bothered now they have got their 23 permanent military bases in Iraq).
My one get out clause for Blair is that his decision gave him leverage in curtailing Bush's worst excesses. British troops initially handled the situation better than US troops and were certainly less tigger happy and the leaked report on how Blair stopped Bush bombing Al-Jazeera is interesting. Perhaps we will never find out the full truth.