Clearly invading Iraq was a bad idea and college senior Matt Yglesias was not only mistaken about believing it to be a good idea but was operating under a number of misapprehensions about foreign policy and American politics.
The main not-totally-obvious thing I have to say about this is that the underrated villains in this drama are the leading Democratic Party politicians of the 2002-2003 era. “Because trusted leaders of my political party say so” is of course not a good reason to back any political position. But the evidence is overwhelming that elite signaling and top-down leadership matter for public opinion formation. I remember quite clearly that in arguments around the dining hall people who were (rightly) opposing the invasion would (wrongly) emphasize the Bush Bush Bush factor in their arguments and I would rebut by pointing to Hillary and Bill Clinton, Dick Gephardt and Tom Daschle, John Kerry and John Edwards. Madeleine Albright. The whole crew.
Since that time I’ve gotten to know a lot of liberal or left-wing people who’ve never liked that whole crowd. Which is fine. Those politics aren’t my politics, but in this particular case that political orientation gave people a more clear-eyed view of what was happening. I saw a sharp partisan disagreement about Bush’s tax cuts, plus a reasonably broad consensus about his Iraq gambit.
So what you learn is that this is a pretty poor heuristic.
On the actual policy, what holds up reasonably well from the old pre-war case is that the Clinton era “containment” policy on Iraq was crumbling. The endless sanctioning of Iraq was not a viable long-term strategy for the region. That left you with two kinds of options. One—the wrong option—was to get more aggressive. The other—the correct option—was to realize that the goal of military domination of the Persian Gulf is just fundamentally misguided. The project is motivated by fuzzy thinking about oil, and it’s been extremely costly over the decades. Protecting Kuwait from a direct and flagrantly illegal cross-border military attack is a defensible (though arguably not necessary) use of military force, but the whole rest of the undertaking dating back to long before Bush was a mistake.