I have a story relevant to this.
As a preface, I'm extremely liberal. Think of the most left-leaning person you know and double it.
One of my oldest and best friends is engaged to a woman who has been variously described as ignorant or racist. She's "earned" this by saying various disparaging things about Indian/"brown" people that have suggested that she has some kind of irrational prejudice. Two specific comments that are somewhat recurring are that she is constantly complaining about how she doesn't want a brown doctor (because she "can't understand them") and that Indians can't drive, a complaint which is nearly ubiquitous where I live (there's a big Indian population so I believe that this particular complaint is borne of a combination of ignorance and confirmation bias). This is obviously not tantamount to saying that brown people are inferior or even that they shouldn't be in the country, but it is a kind of "casually racist" statement that I believe is nonetheless not acceptable and spawned from an ignorant place.
Where this story gets more tricky is that my girlfriend is half white, half Goan, and looks sort of like a really tanned white person with unusually dark hair; you wouldn't know she's from Goa if you weren't told, a notion supported by the fact that everyone seems to believe that she's South American. So my friend's fiancée (then girlfriend) gets into how she doesn't want a brown doctor in the company of my girlfriend (who she thinks is ostensibly from South America), which leads my girlfriend somewhat perturbed. In a highly misguided attempt to ease the situation, my friend's fiancée decides to tell my girlfriend that she's "one of the good ones", which simply annoys her further. It's been a year and a half since that happened and the situation has escalated so far out of control that they're not on speaking terms. Over that period of time, my friend's fiancée has provided plenty of fodder for the argument that she is very ignorant on the subject of race.
Anyway, I'm supposed to be the best man at their wedding and he's a big part of my life. It sounds to me that the OP is suggesting that I break off one of the best friendships of my life to this point, but I've instead chosen to ignore her and lament the negative effects her influence has had on my friend, a decision which has similarly had negative effects on my own relationship.