So what if it is discrimination-based-on-sex? Even a duck's brain is big enough to make important life choices based on sex and it works for them. The extra 1300 grams of brain-packed cranium that we sport is very clever but not clever enough to change what's baked in. Get used to it. The frontal lobe's agenda isn't the brain stem's agenda.
Dictionary.com gives this primary definition of sexism: