Well, let's unpack it.
A lot of what's going on in non-human race descriptions in D&D come from objections of using the same kinds of dehumanizing descriptions as have been used historically to dehumanize other races. There is no literal analog between those non-human D&D races and actual real-world races - just a similarity in description (brutish, savage, primitive, etc).
But the idea of making a historically campaign in which the role of a human culture, one that may have been assimilated into an amalgam culture but still has living descendants, is replaced with orcs or hobgoblins or elves or whatever is literally dehumanizing them within the context of your campaign.
I'm not saying that you're not free to reimagine history any way you want. But you probably shouldn't be surprised at Morrus's response.