there are several issues with this line of logic. One is simply a matter of pragmatic implementation as it would logically lead to 80% of males being kept out of the genepool and yet be expected to contribute to society. This obviously isn't feasible as most males would eventually refuse systemic cuckoldry and revolt. But even if the removal of 80% of males from genepool were to be carried out successfully the sacrifices this would entail along the way eventually lead to the return of a neolithic type structure where no civilization exists at all and warlords keep harems of females and most males die during birth or childhood. If this is the type of existence for humanity that you want then, by all means, be a male feminist (which you seem to be as, going by your line of logic, feminism has actually benefited mankind and should continue to do so in the future by weeding out disgusting inkwells). Your argument eats itself in so far as its consequences would prevent any realistic implementation of it
Another issue is of course that we're rapidly decreasing in genetic quality if we go by the measures of intelligence, testosterone and birth deformities. So it seems that even though less men can be expected to breed in the future, the traits that females are selecting for has a negative bearing on the prevalence of the type of man that anyone that has the flourishing of civilization in mind would want. These half assed appeals to eugenics, when in fact the opposite is happening all around us, are sloppy attempts at masquerading your own weakness and apathy. That, or you're just a foid wanting a dignified excuse for spreading your legs for a new chad that you meet on tinder every new weekend thinking you're doing humanity a favor.