I’d say that having three different words for “because” increases nuance. As the link to merriam-webster’s article pointed out, you get a nuance of formality between “because” and “as”; “as” is somewhat more formal. I’m not sure if there’s another nuance between “because” and causal “since” but smart money is on there being one (if you survey the use of the two I bet you will find there are very subtle differences of usage there – there almost always are nuances of difference between supposedly synonymous words, even if they’re only differences like level of formality).
That is a pretty wild definition of “racism” as “the idea that there are races.”
But I kind of see how you got there.
The idea that human beings can be carved up along certain lines (demarcated by skin color and ancestry) and that there are significant differences between human capability across these dividing lines - and that justifies power differences and relationships of oppression between those groups – those are the ideas behind racism, which expresses itself in oppression and injustice.
But the fact that people do carve up humanity along those lines, and therefore people find themselves put in these categories we call “races,” and have different experiences and opportunities based on which one they find themselves in – that’s a fact. It’s not racist to acknowledge it – indeed, in a way, it would be racist to deny it because it would be denying the reality of oppression.
So “the idea that there are races” = “people are inherently and biologically divided up into ‘black’, ‘white’, etc and this indicates fundamental differences between them” – that’s racism
“the idea that there are races” = “there are ‘races’ because there are structures in the world which are built on the idea of ‘races’ having inherent biological differences, and these structures affect people” – that’s accurately recognizing that racism exists.
Does that make sense?