There's no need to claim that monogamy is morally superior to believe that a gender imbalance is undesirable. That's like saying "well why should most people on

There's no need to claim that monogamy is morally superior to believe that a gender imbalance is undesirable. That's like saying "well why should most people only be attracted to members of the opposite sex?" It's not a matter of should. It's just a fact that most people do, and that this is probably a rather strong instinct (with obvious evolutionary explanations) rather than an easily-changeable cultural coincidence.