Black elves? Ok, at a push there could be some Numenorean blood in there to create such a character. Maybe he has an uncle from Far Harad. I'd be interested to hear the back story, it's certainly not impossible. Or in elven times were people so woke they literally couldn't see how one of them looked quite a bit different? Black dwarves? LOL. It doesn't offend me, I just think it's ridiculously stupid. Why would someone who lives underground need melanin?
Tolkien's whole universe is based around European, and specifically Anglo-Saxon and Nordic history and mythology. "Tolkien is for everyone", hmm, is it? I'm pretty sure Tolkien would have been a racist old white guy if he was around today, and would never sign off on this. He made white lead/good characters, as that was his area of interest. He was making a mythology for England and Europe. There are people of colour in Middle Earth, but in the main story they end up siding with Sauron, lol.
Obviously the producers of these shows don't care at all about lore or staying true to the source material, why would they, it's about making money, so they need inclusivity, because that is the current gravy train. TBH Tolkien was probably turning in his grave when the LOTR film franchise was made. It's an "adaptation" so they will make it for the modern audience. It's understandable that something written in the 50s can't be directly transposed today. The backlash from Tolkien fans will be small compared to the backlash of not casting any actors of colour.