The evidence someone's race constitutes about that person's qualities is usually very easily screened off, as I mentioned here.
In real life, you don't have the luxury of gathering forensic evidence on everyone you meet.
I'm not talking about forensic evidence. Even if white people are smarter in average than black people, I think just talking with somebody for ten minutes would give me evidence about their intelligence which would nearly completely screen off that from skin colour. Heck, even just knowing what their job is would screen off much of it.
Here's the new thread for posting quotes, with the usual rules: