@garretguy I'm clearing all other mentions since it seems we have drifted to a different topic on the desirability or effects of OV itself, and this is unconscionably long--anyone is free to jump in, obviously.
There are several points you made that I disagree with, or are just unclear in the absence of concrete examples or situations, so I'll point those out:
"As a writer, I'm uncomfortable with the idea that I'm not allowed to write something"
Except this is not what OV is about. At the most basic level, you are obviously allowed to write anything you wish. It's just that some--far from all--agents and publishing houses might not publish it. Framing it as "not being allowed" strikes me as untrue to the point of dishonesty.
"because it will be 'harder to market' than if it were written by someone else."
This is an ongoing situation but not for white or otherwise privileged authors. Publishing is still an overwhelmingly tilted playing field, and, e.g. white authors will still have a far easier time being published than, for instance, Black or Indigenous authors. It comes across to me almost like you're saying that marginalized/minority authors enjoy some kind of privilege over authors from dominant groups. If I have misunderstood, please feel free to clarify.
". . . the writings of those seeking to discover themselves, or explore themselves through their words. . . . readers who may have identified with the messages they would have brought will be unable to find someone speaking in their 'own voice.' "
This is the part I found confusing without a concrete situation attached. If the situation is something like a young non-Indigenous author trying to "discover" themself by writing about what it's like to be an Indigenous Two-Spirit person or about Indigenous beings from legend or something, and then became discouraged and stopped writing altogether as a result of being rejected... I'd say in that case they *should* quit writing, because what they're doing is consuming marginalized cultures they don't belong to, and if that's all they want to do with their writing then it's arguably better for them not to write at all. If what you mean is nothing like this, again, please feel free to clarify.
It should also be noted that writing characters from a culture isn't the same thing as writing about the character's culture. I've seen transgender creators distinguish between "writing about trans characters" on the one hand and "writing about what it's like to be trans" on the other, with the former encouraged for all writers and the latter probably best and authentically done by trans writers.
Again, though, there are no hard-and-fast rules and research & beta-reading go a long way to improving depictions. All I'm saying is that people in dominant groups shouldn't kid ourselves that we thoroughly understand marginalized people's experiences and communities, or that we can tell their stories better than they can. It's not about forbidding anyone to write about certain subjects because such a prohibition has never existed for privileged authors and does not exist currently. It's about respect, humility, and the basics of writing as a craft.