I certainly don't claim to have the second sight, but many, much wiser people than me, and whose opinions I hold in high regard, did express grave fears that over a million would die in Iraq and did correctly predict that the consequences of that military action would have serious ramifications for a long time to come.
When GWB declared to the world's press that "the job was done" what he meant was Saddam Hussein had been captured and would be executed, and that America had control of Iraqi oil. That was all he was interested in. During the run up to military action he lied by suggesting that Saddam/Iraq were responsible for the 9/11 attacks on the US.
The so called cover up of the cabinet meeting discussions in which the decision was taken to support the US, I suspect has much to do with the fact that Tony Blair persuaded the Attorney General to change his mind regarding the legality of bombing and invading Iraq and bringing about a regime change.