It's specifically the Velaryon family, not the Targaryens themselves, who are black. While the Velaryons are also Valyrian and share the genetic tendency for white hair and purple eyes, the showrunners decided to make them black as they have always been a seafaring, exploring family and hence could plausibly have some black ancestors. Their skin colour isn't actually mentioned in the books, but apparently Martin did have the idea of actually making them black at one point in the writing process when the Velaryons were intended to have a significantly larger role, so when the showrunner heard that, he considered it a good enough cover for actually doing so on the show. Fair enough, I think.

I don't disagree - on WoT and RoP anyway. That black actor playing a Harfoot commented “They have no trouble believing in a dragon, but they do have trouble believing … a black person could be a hobbit or an elf.” That's an understandable enough reaction on his part, but it's not showing much sympathy, respect or understanding of fantasy fans. Some part of the backlash may come from actual racists, but plenty of fans just figure like you do that in any fantasy work, there is an internal logic to be respected and if you want to use more actors of colour, you can at least try to do it in a way that makes sense in the world in question. Or just pick source material that was more minority-friendly to begin with - such as Sandman, where their more inclusive casting decisions make perfect sense within the context.

Exactly.

Having recently reread WoT, my opinion of RJ's writing quality has indeed decreased a bit (though for the most part he's still better than Sanderson), but I thought his worldbuilding held up pretty well. Of course you can always find points to criticize, but it's very ambitious worldbuilding and it largely works. The most obvious weaknesses coming to mind are ones that many other fantasy writers including Tolkien have as well, like the way most nations have very few if any major cities other than their comparatively huge capital, with suspiciously large armies relative to the population their country can plausibly have.

Fair.

There's another race-related issue in fantasy that seems to be mostly ignored in these debates, which is that in most fantasy series, the different races / cultures are far more internally homogeneous than in the real world: virtually everyone from a certain race/culture shares its typical characteristics in terms of behaviour and interests, with only vanishingly few if any exceptions proving the rule. In Tolkien's case of course there is the fact that Elves, Dwarves, Hobbits, Men, Orcs are different species more than they are different races, so it's more plausible for him - in the interactions between different human cultures, he doesn't really have that problem. But in WoT and many other series, it's pretty noticeable.

In adaptations, such aspects tend to get toned down or removed entirely because it clashes with modern audiences' viewpoints, for us nowadays it seems like a rather 19th century view of the world. Arguably that's a bigger change than the skin colour thing, but nobody's ever complaining about that, which is interesting.

Yeah. Even when it comes to black Elves and Dwarves, those aren't present in Tolkien's texts but they could've winged something based on those Elven/Dwarven communities which are hinted to exist in unknown parts of Middle Earth - but just doing it without explanation is weird. And as I recall, Hobbits are supposed to descend from Men originally, so the lone black Harfoot could be some remote descendant of a lone Haradrim wanderer who somehow ended up procreating with a Harfoot, then his remote ancestor's black skin manifested in him due to some weird genetic quirk, but it's a stretch for sure.

See above, there is an explanation in that case, though apparently it's not made clear in the show itself.