You're attacking a straw man. No one is saying the invasion of Iraq was justified.

One major difference is the motivation for the war. Putin wants to return to USSR borders, which is a motivation of conquest. The US did not want to conquer Iraq. It is not the 51st state.

Another is the regime that existed. Ukraine was a peaceful democracy. Iraq was not. Hussein killed many thousands of Iraqis, too.

The invasion of Iraq was a series of war crimes that should never have happened, but Bush was not nearly as authoritarian as Putin and Hussein is not Zelensky.