The only success story seems to be South Korea, but I would argue they wanted democracy and fought alongside the US for it.
The problem was less with democracy and more with trying to impose a common state on a set of opposed communities that had previously only been “united” in the sense that the one the US was least friendly toward was effectively oppressing the others, and even that might have been successful has the US had needed its own past occupation experience and preserved and reformed state security institutions rather than disbanding them with no transition plan, leading to an internal war before the US even got started with establishing democracy.
Not, to be sure, that that makes the idea of the US trying to impose democracy in all or any part of the territory of the PRC even remotely sane.
I'm not super knowledgeable on the topic, but although the new governments didn't really work out, didn't the mass murders and other atrocities stop with the removal of the old dictator? Those countries may not be "stable" (yet), but is the situation really worse that it was?
Was Saddam torturing a limited amount of dissidents and his sons raping and murdering people as they pleased better or worse than ISIS ruling significant parts of the middle east? Was Gaddafi better or worse than Libya in civil war, slave markets being revived etc? Was life under Assad better or worse than civil war in Syria?
Even with bloodthirsty dictators, there's usually a way to make it worse, and NATO/US is pretty good at finding it.