I guess I just don't care much about defending the sanctity of a made-up universe that ultimately only exists as a platform for entertainment. I've watched the lore for D&D change so much over the years, I consider it more of a fluid than a solid. However they change it, I still think it's cool. I can still have fun playing D&D, whether devils come from the lower planes or from the Astral Sea, whether gnolls are just some normal animal dudes who live on the plains or the demonic spawn of Yeenoghu.
Of course, over time fictional universes change. This is to be expected. There is a difference between the natural evolution of a setting due to the passing of time and a deliberate change made in order to move towards a specific end goal. The latter is much closer to the concept of erasure, which (usually) refers to the replacement or whitewashing of a minority character or group with the dominant group. Sure, it might, "just be entertainment," but we all know that it isn't, "just entertainment," because if it was only entertainment, it wouldn't have evoked such a strong reaction in the OP in the first place. If you can understand how a marginalized group could be upset by not being represented, then its also possible to understand how a not marginal group could be upset due to having something that they potentially feel is theirs being rewritten.
What I care about more than lore consistency is the right of creators to change their IP however they wish. I want the Forgotten Realms to reflect whatever the current minds behind D&D think is the best for right now, instead of just clinging to old ideas.
As I said in my post, I don't particularly care what they do with the setting, because I don't think its a good one :P With that being said, I hate the retconning of aspects of lore in the settings that I do care about, so I will usually take the side which stands against retconning, even if I find many of their arguments to be distasteful. However, it is possible to expand the lore of a setting, without erasing or replacing parts of it entirely. The forgotten realms are huge, there is plenty of space to introduce a new race or subrace, to allow for a better representation of minority groups, without taking away anything from anywhere else.
There are obviously things which can be done without changing the identity of a race, for example, allowing any hairstyle on (almost) any race. I say almost there because I am pretty sure that if you had horns like a tiefling, some of your hairstyles would be incompatible with other races, but they are the exception and not the norm. Things like changing the structures of the face of a race however, or its cultural background, would be undermining what that race is to begin with.
I want the people who are currently making content for a setting to be free to make whatever alterations they need to in order to tell good stories today, without the fandom losing its shit over minor details.
Minor nitpick here, but I personally believe that the truly great stories are stories which are timeless and can be told in any era. A literary masterpiece isn't something that suddenly "goes out of fashion," because it tells a story which is universal, but I do get what you mean. The forgotten realms is not however, one of those settings that qualifies as a literary masterpiece.
Even more important to me than that, however, is that these entertainment properties that we all enjoy are serving their audiences well. All of their audiences. Not just some of them. And that they're telling stories that serve the world well, telling them in ways that make the world better, rather than worse. And inclusivity is really important at this turning point in our history. But it's not even about the abstract "social issue" of diversity or the "prevailing politics" and trying to appease some agenda. It's about people like Saturdiva and their personal, heartfelt desires which have been ignored for so long. And even when she asks, nicely, sincerely, for something that is long overdue, no one hears her. They just come in to debate the "topic", to go on and on about how important The Lore™ is, but I don't see anyone actually responding to what she wrote. I don't see anyone acknowledging that they even heard her.
It is important to me as well and I do believe I even addressed her post (although I did not directly quote it in my response). It is just that I don't believe representation in a fictional universe is a zero sum game. You do not need to take representation away from one group, in order to allocate it to another. There is always room to expand the setting and in doing so, you can elevate the setting in the process. Whereas, if you are retroactively rewriting the history of parts of the setting, you are almost always going to be making the setting weaker overall and step on peoples' toes in the process.