Liberals tend to not look at things in terms of right & wrong, or moral & immoral. Invariably they filter events through a prism that looks for strength & weakness, power & powerless, etc.
They apportion their sympathy to whoever is weak/inferior/underdog, based on their worldview. So for them, it's as if being the weaker in a conflict imputes some nobility and moral rightness.
They relfexively side against the USA because it is powerful: to them, the weaker adversary is the one worth supporting, even if it leads them to make suicidal decisions.
Yes, at least they say they are in favor of the weak and oppressed. It makes a good excuse. But, paradoxically, they have to become powerful in order to help the weak and oppressed, so they use that as an excuse to justify their power madness.
It's much the same paradox compressed in Marx's phrase, "the dictatorship of the proletariat." The weak have to become strong and brutal, or at least their privileged advocates do, who therefore call themselves "the vanguard of the proletariat."