[inglor_cz]

"Having fewer opportunities is obviously a harm."

Scope matters. On the level of the entire economy? Possibly yes, but you haven't shown that the entire economy will discriminate against X or Y; respective preferences of individual players may well balance out.

On the level of a single Acme, Inc.? What if that particular organization is unofficially hostile to a particular gender? I would say that in such case, it is more harmful to join it blindly and then suffer from the generally unfriendly environment than to steer clear of them in time.

I wouldn't personally like to become an employee in a corporation that prefers not to employ men and is only forced to do so by external powers. And I would prefer them to be honest and advertise that openly, to save my time and theirs from making an unhappy match.