OK let's hear from the Sunnis and Shiites now
Or the hundreds of thousands dead Iraqis
I've got the UN polls right here and by 2007 most Iraqis hated American troops. But of course by 2014 the public was split about whether the US should have withdrawn at all! My position is that I think there was serious mishandling of the reconstruction of Iraq, Paul Bremer should be in jail, etc. But I hold out hope that there was a right way to do it.
There obviously was a better way to do it. Or at least avoid taking certain actions that were undeniably destructive. But IMO that gets to part of the heart of the problem with the situation altogether. These were people with surprisingly shallow(with a mix of corrupt) ideas on what needs to happen after you have created the philosophical rationalization to justify preventive war and wholesale regime change. And the State Department and the intelligence agencies tried to warn them of their own ignorance, but there was no avoiding their arrogance in it.
And it was already a long response for a place like this, but Syria and Iraq are materially different. Syria, by every metric we have, would be a much more difficult task if you subscribe to all-in commitment to oust Assad, secure the country, and install a democratic system of government.
One of the arguments for why things could of gone better in Iraq under different leadership was because of the unified and initially cooperative military force outside of the loyalist Republican Guard and the largely cooperative Ba'athist bureaucracy. That had you been more sensitive, aware and proactive in the dynamics of those relationships, you could of fostered a much smoother transition and had a lot more resources and trained security forces to deal with a much smaller insurgency of Al Qaeda fighters/Saddam loyalists that would likely not be able to recruit much, if any, Ba'ahists or military forces. Though to argue myself, the sectarian divisions were always there(which is part of why strongmen were supported to secure often at-odds factions within borders, because they kinda work in that regard, at least temporarily), so there still is a fairly decent probability that those tensions were bound to bloom regardless, and that civil war would still be hard to avoid.
That is really not the case in Syria from everything we have seen. The country is embroiled in a civil war already, tensions that have continued to grow since the Arab Spring, and the divisions run deep, and there is anything but a unifying social and structural fabric to lean on that would make the potential transition a smooth one. So aside from the points others have made about the obvious differences, I think tactically there is a lot more uncertainly and risk in Syria, and likely that is also why(along with geopolitical issues) two administrations, and the military, have now been hesitant to escalate to that sort of strategy.
