Racism is probably the first pseudo-scientific theory to gain widespread currency. Roughly a century ago, everyone who was educated was a racist. It offered a supposedly natural way to deal with difference between ethnic groups (the English gravitate to constitutional monarchy, the Russians to authoritarian tsars because it is "natural" for them).
As for the actual Science behind race it is very, very simple. There is one race for humans, unlike, say felids or equines where there are bona fide several. Humans almost died out about 75,000 years ago and as such we are probably one of the most homogeneous animal populations on Earth. So, someone who claims to be for "racial harmony" is bolstering racism then taking on the mantle of benevolence for being able to overcome it. Much of the result of promoting diversity, therefore, is perpetuating defunct pseudo-scientific social theories. This is the modern bureaucratic version of having people dig holes in the morning and hire others to fill them in during the afternoon.
To be blunt, racism has much more political pull than one would have expected, since it managed to transcend nationalism (which is bad, remember????? "greater Germany" is so much more appealing than a welter of small states in central Europe). Bad behaviors of some other group or country are explained by a theory that leaves them as congenitally inferior. The point is that it should be seen as the result of lots of hard work by intellectuals (mostly European, since the US was too much of a backwater to do that by itself) and then power-grabbing politicians. This is the cautionary tale about pseudo-intellectual movements that get a political life of their own.
In more recent memory, global warming advocacy is heading in the same direction, with all sorts of political/social agendas suddenly being "backed by Science". FWIW the Science of global warming is pretty well understood and people like Al Gore get it so (on purpose, I might add) wrong it hurts. This is not a dig at Science at all 9which is much more boring than people want to admit), but noting how Science gets conscripted in the service of other things. About 30 years ago, it was fashionable to claim an Ice Age was impending and calls for nationalization of industry and agriculture (the usual Progressive dogma) was now firmly backed by Science. That petered out, obviously. And Malthus' dreary assessments proved that Fabian Socialism alone would save us in the late 19th century.