i think there's a much broader discussion to be had here.
we can't ban racist people from existing, stopping a racist person from using a word, any word, in a derogatory way is not magically going to make this person less racist. if the intent behind using such words was to convey a racist or demeaning thought, then it's the intent that matters, nothing else.
i think if it truly was an accident and in a private conversation, then there's no reason for the guy to be banned. i'm more scared about thought police than people having racist thoughts. i'm pretty sure i've had them sometimes in the past and hope my better judgement helped me realize later on it was irrational to have those. in the same way i'm pretty sure plenty of people had racist thoughts about me and that's ok. it's part of human nature, one that we should continuously strive to be better about. hiding it, or pretending it doesn't exist will never solve the problem, instead will make racist people even more defensive about their "us" vs "them" mentality.
That's the thing it's not being hidden it's being punished the's a difference like it or not that's the only language some people understand, a number of people only began to fear being outed as racist when they faced retribution for their actions these people will always be defensive and have that us vs them mentality as their beliefs are built on a notion that they're superior and now have to share the same rights as others.
I also don't buy it's part of human nature, preference is not racial bias as put a bunch of young kids together they won't hate each other because they look different if anything they're more fascinated by it (an example is that story on social media where a young white child wanted his hair cut short to look more like his black friend) racism is something that is taught.
But that's my point exactly, it's not actually solving any problem, if anything it's making things worse because someone is not going to be any less racist because they were told a word was "bad". It's not the word that is bad, is the sentiment of feeling like someone is superior due to any "x" arbitrary factor like skin color.
Education is the only way to open someone's mind to something new. Being exposed and interacting with different people is how you soften people up and have them realize these notions of "us" and "them" are just made up nonsense. The more you try and ban certain words, the more defensive you'll make such people to change their minds. And I also take objection to the notion of "being offended". That concept gets thrown around way too often and I have absolutely no connection to it. If someone says something absurd it's the easiest thing in the world to ignore that person.
Also, on your last point, i was more refering to the idea of tribalism, race is only one form of tribalism, but there are many others. Like feeling a deeper sense of empathy with people that live physically closer to you, nationalism, etc. All these feelings are quite natural and part of our evolutionary background. It takes modern sensibility to be aware of them and actively fight against those feelings.