But that's how sexism and racism and any kind of discrimination works in the human mind. There are innocuous traits, like sex and skin color, but also many other traits, and we use them to make predictions about behavior. This is unfair discrimination; fair discrimination looks directly at the behavior of an individual, not some innocuous proxy for the behavior, even if that proxy is right 80% of the time.

For example, most people who have an account throwawayXXX on HN are using it temporarily to say something. However, I actually kept one such account for a long time. My username is an innocuous trait, but you're discriminating if you assume my motives and behavior will be like most of the other throwaway accounts, just based on my username.

That said, I believe unfair discrimination is unavoidable in life because we can't always wait around to see what an individual's behavior will be before we discriminate fairly. We couldn't function without stereotypes and assumptions. And so, while still unfair because of the potential for unjustified penalties, it's much better to look at many variables than it is to look at one or two.