Okay, let's go down this road. I think you've touched on something important, so I genuinely want to get this.
How have the left played a "huge emotional role" in the polarization? I suppose you could argue that "the libs" or progressives have essentially started to shun those who they find don't agree with them on certain key issues (abortion/birth control, immigration, etc.).
But how does this differ from how political discourse has been for the last few decades? People want to act like cancel culture is this new thing that Millenials invented, but societies have utilized shame in order to shun unwanted or undesirable opinions forever. Really, the only thing that's changed from my perspective is that people have started drawing lines in the sand, and conservative reactionaries stamp all over the lines, then go Pikachu-face when they're boycotted.
I appreciate the anecdote, because I think it's happened to all of us. I had a similar interaction with someone who balked at my usage of the word "homeless" (I live in a city, so it's come up once or twice), insisting that I should instead call them "unhoused".
I think the important point in your anecdote is saying "it's unsettling and angering to be called out for doing/saying something racist when you in fact are not racist". My stance on this issue is that everyone's a little bit *-ist. Instead of concluding "people can do and say racist things while not being racist", I think a more helpful conclusion would be "people do and say racist shit all the time without meaning it because we have a lot of racism built into our brains".
I agree with you on the othering, however. I dislike when people try and put racists, sexists, etc. in a timeout corner, mostly because it seems to be with the aim of declaring themselves A Good Person rather than actually affecting any social change. I think it's more helpful to say "hey, look, we're all born with a lot of baggage from our environments and parents, and we don't get to choose how our brains are molded".