From my understanding, the premise of revolutionary defeatism involves supporting the defeat of your own bourgeois government. I am an American. I am perfectly fine with that when it comes to things like US military actions in the Middle East. However, there has been one enemy the United States has had that is definitely quite different, Nazi Germany. It's pretty much universally believed among the left that Nazi Germany was bad and should never be supported (and that's for a GOOD reason).
But how does revolutionary defeatism square in with something like that?
The communists and KMT allied with each other - perhaps forcefully - to defeat the Japanese because otherwise there would be no China to fight over.
Resistance against Nazis throughout Europe did find strange coalitions of communists, liberals, and even conservatives. But as you can see, after WWII liberals never sided with the communists during liberation movements. Usually they were working with the west to undermine everything at home and fascism was usually the result