In traditional society, women were strongly encouraged to refrain from sex before marriage, and marry responsible men with good jobs who were able and willing to support a family.
Today, women are encouraged to follow their hormones, which tends to result in them have offspring with a long succession of sexy males who disappear, often into jail or dying violently, and who often rough them up and steal their money before leaving.
Bryan Caplan correctly argues that the non traditional family does not necessarily harm children, because the low conventional success rate of children from such families may well reflect them behaving like their fathers, who have a different standard of what constitutes success, and may well be very successful by that standard – more chicks banged, less time wasted from nine to five, and more enemies maimed. Further, women who choose to have a non traditional family presumably prefer it – there can be little doubt that the sex is hotter the badder the boy.
Now this is a good deal for alpha males, and lots of women argue it is a good deal for women, but it has a sizable externality, in that it encourages male behavior that causes problems for other men, and produces children that cause problems for other people. Bastards are bastards. The production of bastards creates large external costs. Encouraging fidelity, chastity, and female preference for responsible mates, even though their hormones tend to cry out for demon lovers, reduces other people’s costs – in traditional society the costs to fathers, uncles, and brothers of grown women, in modern society the cost of the welfare state, in all societies the cost of crime.
The welfare state reduces the costs of hormonal female behavior to parents of those females, since the cost of bastardy is externalized to the rest of society to a greater extent, and thus reduces the incentive of parents to inculcate their daughters with traditional values and deprecate the natural behavior of females – the natural inclination of women being more towards the demon lover. Women can be socialized, pressured, and monitored into fidelity to males that materially support them and help raise their kids, but it takes a firm hand and a watchful eye. While Islamic society takes this to extremes, the other extreme, total neglect of this problem, has costs also.