Not going to like, the definition of racism there makes sense to me. Racism being a set of racist policies resulting in inequality based on racist beliefs. I mean, how else do you describe what race-based slavery is? Slavery is a policy resulting in literal enslavement based on the idea of black people's inferiority.
Like, compare this to ableism-- disabled people often are not allowed to get married because, in order to receive support in society as a disabled person, disabled people are not allowed to have anywhere near the personal worth of an able-bodied person. There's no way this came about completely without some fucked up ideas about disabled people. I also see no way to discuss how this policy came about without bringing up a society-wide acceptance on the lack of worth disabled people "should" be allowed to have.