"Meritocracy" is almost always a flawed idea, because it relies on the principle of those in positions of authority choosing the best candidate for a given role; the key word here is "best." That's a subjective term, and usually favors a small set of criteria over a more holistic view. People, with some exceptions, are bad at seeing the big picture.
With very few exceptions, I will always favor candidates with broader experience over those with narrow strengths.
That's the whole idea. When you need a surgeon you don't need a specifically sexed, or colored, or whatever surgeon. You just need a person good at the "small set of criteria" of performing a surgery.
Eg. Imagine if I was at the top of a burning building and my family needed rescued. I would want 5 men to try to save us, not 5 women. Does that make be sexist or normal minded?
EDIT: and off course vice versa for tasks that women are best suited.
Only the pool has to be created in the lower levels (education etc) not imposed at the company level with less good candidates favored just because of their sex.
>Until such time as that happens, "sex discrimination against men" is impossible.
It's very possible, if meritocracy is sidestepped, and the person who gets sidestepped is a man in favor of e.g. 50-50 parity with a woman.
Unless the pool entering the workforce is 50-50 already, then 50-50 hiring requires discrimination.