Calling a black person a "nigger" isn't racism -- but (outside of specific contexts that weaken this conclusion) its a pretty strong indication of racism, and (subject to pretty much the same contextual considerations) not addressing it normalizes racism, whether or not the actual utterance was motivated by racism. The same is true with "woman", "bitch", and "misogyny" in place of "black person", "nigger", and "racism".
> And what OP did is white knighting, i.e. a man defending a woman, because she's a woman, in order to appear virtuous.
I don't see any indication that it was done "in order to appear virtuous", which is, you correctly note, an essential feature of white knighting.