I agree with
@doctorbadwolf here, this is a bit of a stretch. They're not making the Drow culture be good, they're letting them be more diverse culturally. They're showing that Drow don't have to be the evil, Lolth-worshipping, spider-loving elves of previous editions (granted, most previous editions had multiple exceptions to this. 4e specifically made Drizzt be the only good drow, which is a very strange and bad change, IMO). From what we've seen, they're not
making Drow be good, they're
letting them be good, and also lightening up their skin to get rid of the connection between dark-skin and being evil. Drow can still be evil, they can just also be good, and are including more examples of good ones as we have plentiful examples of bad ones in the art of 5e.
If they were to have their skin color change to be white and also make all of the drow be good, that would be one thing, but that's not what they're doing. Go look at the OP, and you'll see that this is true. In the second image of the Tasha's Drow, there is a very clearly bad/antagonistic Drow that is fighting Vi atop of a Lightning Rail.
It's not "Dark equals bad" and "Light equals good", it's "Dark doesn't mean bad" and "Light doesn't mean good". I also am assuming that they'll leave Deep Gnomes with dark skin, which are a pretty neutral/good-ish race with pretty dark skin.