andrewducker | In the interests of inciting useful debate

cairmen says:
OK, devil's advocate moment here, and please, please believe I'm not advocating for discrimination against mothers or pregnant women:

Why not?

We don't have a choice about our sex, fair enough. We also don't have a choice about our mathmatical ability, but I'm allowed to explicitly discriminate on that basis - if I'm hiring someone for a position requiring mathematical knowledge, I can totally say "you just don't have the maths aptitude. Sorry. Goodbye."

I can discriminate based on social aptitude (and we don't have a lot of choice about that either). I can discriminate based on random chance ("Oh, you worked with Bob? Cool. You're hired.").

What's the key difference here?

Would anyone care to go here and _politely_, in clear language, tell him? It's a discussion on my journal, so no flames please.
(Turning off comments here, so that you have to go there instead)