Hindsight
I've always hated the "if we knew then what we know now" rationale for opposing the war in Iraq. The problem that all of us who were right about the war had with it wasn't that it would necessarily go poorly - although that was also on the table, what with the outside force invading and reshaping a society through no desire of their own - but that the general idea of using bogus information as an impetus to preemptively invade a country was a bad idea on its own merits, even if it ended up with us sitting on piles of gold and barrels of oil as we high-fived Ahmed Chalabi at the new Chuck-E-Cheese in the middle of Tikrit.