One specific and relatively common version of this are people who believe that women have a lower standard deviation on measures of IQ than men. This belief is not incompatible with believing that any particular woman might be astonishingly intelligent, but these people all seem to have a great deal of trouble applying the latter to any particular woman.
I don't think that this requires a utility-function-changing superbias. Alternatively: We think sloppily about groups, flattening fine distinctions into blanket generalizations. This bias takes the fact "women have a lower standard deviation on measures of IQ than men" as input and spits out the false fact "chicks can't be as smart as guys". If a person updates on this nonfact, and he tends to value less-intelligent individuals less and treat them differently, his valuation of all women will shift downward, fully in accordance with his existing utility function.
Placing "a high value on not discriminating against sentient beings on the basis of artifacts of the birth lottery" is not a common position. Most people discriminate freely on an individual basis. They also aren't aware of cognitive biases or how to combat them. Perhaps it's safer not to learn about between-group differences under those circumstances.
Strange advice for Less Wrong, though.
One argument you could give a Less Wrong audience is that the information about intelligence you could learn by learning someone's gender is almost completely screened off by the information content gained by examining the person directly (e.g. through conversation, or through reading research papers).
A few examples (in approximately increasing order of controversy):
If you proceed anyway...