Shorter version: nobody has any fucking idea.
I used to spend some time trying to figure this out. Those of us who were against it were against it, in part, because it didn't make any fucking sense at all. The nation was gaslighted by the Very Serious People who had no idea why the fuck they thought this was a glorious adventure.
The stated reasons were bullshit, the implicit reasons were gibberish. Yes you can chalk it all up to OIL or making the military industrial complex rich or whatever. I'm not dismissing those reasons. But everybody seemed to have their own reasons. For Christopher Hitchens it seemed to about the Kurds. And punching hippies.
Left blogs thrived largely because it provided about the only place we could gather and say... uh, you know this is crazy, right?