So a few quick points of clarification regarding certain points above and then a quick general thought:
Fandom did make a change to our Community Creation Policy - https://www.fandom.com/community-creation-policy - to prevent deadnaming - that clause can be found in the "Living People" section. Our Terms of Use makes clear that the Creation Policy is essentially an extension of our ToU and covers what you may and may not do on our service. Additionally our ToU prohibits "transphobia" - I'll go into more detail below as to why deadnaming is a form of transphobia.
I'd also clearly state there is a significant difference between a fictional character and a real-life individual. We're working right now on a style guide for communities on how to handle fictional characters in the broad realm of gender identity - I acknowledge that if a character's deadname and/or any other form of identity recognition is a major plot point in a movie or game, it's not realistic to ask that the deadname (or whatever it may be) not be used at all. How to do so tactfully is something we're discussing.
Insisting on calling someone by a deadname even after that individual has clearly stated what their identity is isn't "an insult", it's harassment. Period. That's why this policy is in place. If I went up to someone and introduced myself as "Tim" and then they went around loudly introducing me as "Patrick" to everyone and insisting my name is "Patrick" no matter if I try to correct them, I'd feel harassed. And this silly example lacks the context of an individual being transgender, a community who faces hostility and outright threats just because of how they identify.
We broadly reject the description of not using deadnames as "historical revisionism". People's security and mental well-being matters more than documentation.
Look, I've edited wikis for 15 years, almost entirely focusing on IRL documentation of subjects. I also minored in history in college and my "outside of work" hobby is dedicated to historical research. So I can empathize with the deference to canon and desire to create "complete" pages. To be told something shouldn't be put in an article, regardless of its accuracy, is something that is somewhat antithetical to the general wiki culture that stems from Wikipedian norms.
All of that said, I personally find the argument that having to use a deadname in an article because that's how it was referred to in contemporaneous credits or literature as absurd. There are loads of examples of non-transgender individuals who changed their name - even aside from the obvious married name examples - and I rarely see people insisting on naming a wiki page or referring to them by the original name. For example, the famous novel "The Running Man" was attributed to a "Richard Bachman". But Stephen King later came forward as the author. I don't see any encyclopedic references to "Bachman's writing style". Heck, typos happen in crediting - no person in reasonable good faith would assume they insist on using the typo-ed name as a page title on the wiki.
So I don't understand why using a deadname is different from any of the above examples. The person is the same person they've always been, and their personal identities - how they view themselves - has not changed. When an individual shares publicly that their name is different than how they've previously identified, it's not because they just woke up some morning and said "I am now X, let me go announce it". It's because they've decided to share something deeply personal about themselves, something they've known to be true for a signficant period of time if not their whole life, to a wider audience. And if someone on the internet insists "No, 20 years ago this movie I watched said you were X so you are always and forever X and I won't let anyone forget it", it is incredibly disrespectful at a minimum of that person.
