Okay i see what you mean.

But then you can also ask, why are boys valued more than girls? Or blonds more than brunettes? Or dimples more than no dimples? (My cousin had *@#$%&@ dimples!!! Everybody was ALWAYS commenting on them.)

So yes, it is societys norm for children to have two parents. I mean, it TAKES two people to make a baby. So society expects both parents to be responsible for that baby. Otherwise society has to help raise the child. More or less.