Biologically speaking, with humans the maximum rate of population growth has more to do with the number of women than the number of men. A single man produces sufficient amounts of gametes to impregnate quite a number of women in a relatively short amount of time, while a woman is indisposed at least nine months per ~1 child. With a sperm bank and a large amount of women, potential population growth rates can be higher than they might be if the women were less. So, men are more expendable when it comes to repopulating the conquered planets.