secretary o'neill (a centre right republican) who was removed in Bush's first year in office, stated that one of the first things on the agenda was to get rid of Saddam. (many in that neo-con crowd were saying that for years- I remember seeing a documentary after the gulf war in 91, Wolfowitz claimed Saddam was 6months away from making nuclear weapons, then again in 2002 saying the same thing (Saddam is 2years away from making nukes)

the fact is they needed a reason to go after Saddam, and a US public
still feeling the shock from 9/11 was more likely to support a war if there was a possible threat to the US - even though the only link
between 9/11 and Iraq - was a possible meeting between Atta and an Iraqi embassy official in Prague (something the Czech Secret service - has since denied - and yet Dick CHeney still brings it up.

I think Bush & co. decided that they would worry about whether or not there were any wmds after the war - and figured people would quickly forget - (have you listened to Dennis Miller lately?).
The fact is secrets are hard to keep, if the US faked them and the truth came out - Bush would definitely find himself in a can of peaches. Its a lot easier to say, I guess we were wrong, but Saddam was a tyrant and the world is better off without him.

- the real reason may have been to establish - a democratic model in the middle east so the other countries in the region have a model - although that may have been an infantile fantasy.