There mere fact that there are "evil" or "savage" races in the first place is the really the root of the problem. Its interesting to see that all the descriptions of sapient "evil" races match what colonial europeans used to justify their conquests. I'm sure other conquering countries in the past used the same whenever they attacked other civilizations.
Same old story. Dehumanize the Others, make it morally acceptable to attack them and take over their lands... I mean, let's look at orcs one more time. According to the background story, they literally had any chance of a home taken from them by the other gods. Really, the orcs were screwed over from the beginning - we reach our children to share, but dieties can't?
From that basis, associating others, like half-orcs and tieflings and dragonborn as an extension of the "savage" races is pretty common. in fact, its pretty much how our brains as humans are wired. Is it any surprise they're often called monsters? They're literally in a book that's labeling them as monsters. Half-orcs are part of the orc writeup. Drow, despite being a core book PC race, is likewise labeled as a monster. Tieflings are the children (or otherwise have the blood of) the worst monsters of D&D, the fiends. And dragons... color coded for your killing convenience. You literally can tell if someone is evil by the color of their skin.