The thing about anger is that it is not a very nuanced emotion. I see a few different points related to your essay:
- Authors who write about characters who are members of a different gender, sexual orientation, or race is cultural appropriation.
- Authors who are white have an advantage over minority authors and, when they write about minority subjects or characters are perhaps unconsciously appropriating market share.
- The author was dismissive of the complexity of the subject and appeared condescending and superior which seemed to closely parallel the attitude of the 19th century colonizer.
Point 1 appears absurd and may not be your intent but is what I think people are responding to. Identity politics run amuck. Point 2 is more nuanced and worthy of conversation. Point 3 goes to show how we talk past each other, to the bogey man we create in our minds instead of to other actual people.
The irony of this is that fiction today, in literature and film, often lacks any nuance or resemblance to reality. It is almost all appropriation, and perhaps is at a deep level — which Plato recognized; his concept of mimesis is already twice removed.
I think it was Walker Percy who said all great literature is regional literature. Although I find the idea of censoring an artist in any way whatsoever ethically and morally repugnant, there is some truth to that. There is often a rish to judgment or categorization on either side of this debate, but the devil is in the details.