Of course I don't know if Keara or Guido knew any of this, but it certainly feels to me that the commit message is ostracizing an entire family line because they had the misfortune to have the wrong last name. In fact, it seems like Strunk & White is making changes to be inclusive in its advice -- exactly what I would have thought we wanted on our side ("our side" being the diverse and welcoming side).
The claim in the commit message that the Strunk & White style contains relics of white supremacy might be fair or it might be overblown. I don't know, I'm not an expert. Your research on the updated editions and evolving advice looks good. (Just note that the most popular edition for people to find is very old because it's in the public domain.) In any case, saying that Keara and Guido mistook the family name of one of the authors for skin color feels derogatory.
The commit message clearly is controversial but when you say the change itself was unnecessary, consider that English is now a language predominantly used outside of USA and Great Britain. Relaxing the recommendation to use S & L Standard English in the CPython codebase isn't problematic in this sense. That recommendation was largely ignored anyway, as core developer voices in the other threads already admitted. So, chaos won't ensue. We still want to maintain consistency, as PEP 8 recommends. I don't think you have to worry now about seeing organization and organisation in the same docstring.
That's what it felt like: betrayal.
This entire section of your message is confusing to me. Mind explaining? How does a commit message equate stabbing somebody who helped you? What is being betrayed in this commit?