I don’t see how a non-invaded Iraq would have been any different than Libya. Had Bush kept Iraq under sanctions and done nothing to oust Saddam, all we’d see is McCain and Obama talking about the “plucky” guys, like al-Zarqawi, fighting Saddam for freedom in the Iraq Civil War. As Saddam would bomb them, we’d retaliate much like Libya by attacking Saddam’s forces.
I believe quite some time back, some folks decided this was the way things were going to go. Their motivations... up for debate. But here we are dealing with it.
The problem with Iraq was that Bush didn’t follow through, as usual. He let them enshrine Islam in their constitution and didn’t impose a serious occupation. And then Obama undid everything.
Iraq had a relatively educated populace, the West had many friends, and Saddam was a basically secular dictator interested in imposing his version of Iraqi nationalism, meaning that some of the people he killed were in fact Islamist nut jobs interested in turning Iraq into a part of the new caliphate (whatever they thought it was). That is, we could have tapped into his capable people, imposed the peace, and restructured it.
But we blew it because of the pro-Islamic left, since Bush was a guy who couldn’t even stand up to his own shadow.