If half a million men are killed there can still be as many babies born to replace them.
If half a million women are killed (probably would be more as they are physically slower and weaker) then fewer babies will be born.
Did you or your sons ever learn biology OP?
I do find this line very distasteful and reductive. If we're talking about livestock on a farm, then of course you only need one or two bulls/rams to 'cover' hundreds of cows/ewes.
Are we really trying to say that we would view human women in basically the same way: happy to 'play their part' and be 'serviced' at will by any of the limited stock of men around, who will then disappear, leaving them to bring up the children and move on to the next woman in the line - just to populate the country, with no sense of relationship, morality, family, society or humanity involved?
Although, biologically-speaking, a man could father hundreds more children than a woman can give birth to, we as a species expect them not to - and to stay focused on parenting their own children. The selfish, deadbeat ones who don't behave this way are rightly criticised - but using this argument, they're actually the good, wise, socially-responsible ones; far more so than the 'irresponsible' ones who do act as proper fathers and don't just flit around impregnating woman after woman and then abandoning the women and kids, in an endless cycle.
Is this really what we would view as an acceptable way to go about things - reducing humanity to the level of animals and women as nothing more than breeding stock? If we don't, I don't think it's an argument that we should be holding to - it just cheapens all of the other very valid arguments that it is placed alongside.