Konkvistador:

In a way monogamous norm is sexual socialism for men.

That's a good way of putting it -- and it leads us to the fascinating question of why people who express great concern about inequalities in material wealth under economic laissez-faire almost invariably don't show any concern for the even more extreme inequalities in matters of love and sex that inevitably arise under sexual laissez-faire. I think a correct answer to this question would open the way for a tremendous amount of insight about the modern society, and human nature in general.

Michel Houellebecq has an interesting paragraph about this issue in his novel Whatever:

It's a fact, I mused to myself, that in societies like ours sex truly represents a second system of differentiation, completely independent of money; and as a system of differentiation it functions just as mercilessly. The effects of these two systems are, furthermore, strictly equivalent. Just like unrestrained economic liberalism, and for similar reasons, sexual liberalism produces phenomena of absolute pauperization. Some men make love every day; others five or six times in their life, or never. Some make love with dozens of women, others with none. [...] In a totally liberal economic system certain people accumulate considerable fortunes; others stagnate in unemployment and misery. In a totally liberal sexual system certain people have a varied and exciting erotic life; others are reduced to masturbation and solitude.