Shouldn't be relevant as an issue, but I see it as a legal structure to support 'couples' in raising children at its essence, and in reality that has nothing to do with sex, nor even gender, of the parents. And indeed children come and go, and sometimes don't come at all - so for practical purposes just a type of contract between two consenting adults about co-living and co-dependency. With its purpose to enable sharing of resources in a defined manner such that if can offer measures of security, which enable trust, and therefore promote greater individual success, for the power of a couple can be higher then that of two individuals - but done so within, understood by, and accepted within the society. With that though, like anything that involves responsibility, comes with it the potential for abuse, neglect and disintegration.