the biggest problem (among many) with the Bush (and ace) cowboy approach to foreign policy in general, and overthrowing Saddam in particular, was that they completely ignored the likely consequences.
sectarian violence at a level never seen before in Iraq...and by some measures, more civilian deaths in 5 years than the 20+ years under Saddam.
massive numbers (millions) of displaced persons, mostly the Iraqi middle class
the worst public health crisis in Iraq in 50+ years
a new "cause celebre" for terrorist recruitment
a stronger and more influential Iran in the region
All of these outcomes were predicted and ignored in pursuit of a rigid ideological goal or personal vendetta.
To what end?