"You're racist!" is an attack.
"That thing you just said was racist." is better but will still come off as an attack.
"Have you ever thought about how what you said will impact [minority group]?" will work much better.
To summarize: PC phrasing works better among people who voted for the anti-PC guy? I'm not disagreeing with your thesis, just pointing out that it's not obvious that it should be the case.
If it's the former, being called a racist is a valuable thing. It's somebody telling you that you have advertently or inadvertently acted in a manner that is prejudiced against an ethnic group in a way that perpetuates societal imbalances (racism). Now you get an opportunity to fix it.
Apologize, then stop doing what you were called out for. Now you'll neither be a racist or called one.
Great! Everybody wins.
The reaction of, "How is it racist?" can be taken as a defense even if it is an honest question.
Luckily, words are amazing and there are ways to diffuse this stuff. "I think some folks might find that insensitive, you know" might be better wording than "That was rather racist" - even though I might prefer the more direct version. Likewise, the response can be reworded for different effect as well.
I'm not sure how to complete this thought right now, but it comes down to: "Do you feel safe expressing yourself?"
Your "safety" might not be important for the situation, may not be relevant for the situation; safety shouldn't be confused with agreement / support, etc, etc.
I mean "safe spaces". Of all the problems facing our world today, how did having a place for students to go and chill out on bean bags become a rallying cry. Why this obsession with student activitsts in general, who as far as I can tell have been caricatured as out of touch poseurs for literally decades without it escalating into a full on culture war.
Do people really not see the irony of complaining about political correctness when stats generated by government departments are being discounted as "fake news" by the president?
From the outside it really does seem like insanity, but I have to assume people literally believe these things to be important for some reason.