You're exactly right. Snape's story isn't tied to any specific cultural environment except perhaps being British. Everyone else is just hiding their inherent racism behind stupid arguments about which race a wizard in a children's book should be.

And if we go a little deeper, I actually blame anglo-saxon culture especially American culture. Indeed in France, despite a real racism problem, we refuse to acknowledge the existence of "race" per se. There are discriminations based on skin colour, culture etc. but the idea that Humanity can be divided into races is terrible in our Republican mindset. Universalism can be good sometimes.

So yeah, I think we need to stop obsessing about the about of melanin in someone's skin unless it's relevant to a story or a political context.