"Very unfortunate" is a real understatement! At my most frustrated, I would say that we took a brutal, broken, state and replaced it with one which although not as obviuously brutal, is far more chaotic, and quite possibly more broken than it was before we boot boots on the ground. that's not simply unfortunate, that's bad.
As to what we were thinking, i think that depends on the year. even if in '02 and early '03, we really thought that the threat of WMD was real -- a premise i am willing to accpet -- it became clear that we were wrong, and that having been wrong about that, we should have been talking exit strategy by late '03, not "victory". As to what was accomplished, it really not clear, at least not when weighed against the losses we sustained -- most importantly human, but also financial.