You're assuming that people do what they want. This is a similar argument to the idea that homosexuality can't be genetic as if it were then the gene would have

You're assuming that people do what they want. This is a similar argument to the idea that homosexuality can't be genetic as if it were then the gene would have died out. That's not true because basically for as long as culture has existed there has been pressure to conform to a societal norm which generally involves male / female relationships and children. As a result of that many (though not all) people instead of doing what they want have done what society expects of them. As it goes I think you're right that it's the norm in as much as I think there is a biological imperative there (anecdotally having kids I can vouch for this), but I think your logic supporting the argument is off.