I also love the casual assertion that “marriage is by nature the union of a man and woman,” as if marriage is some sort of naturally occurring phenomenon like evaporation or mitosis. Marriage is a social construct. It’s whatever we say it is. And it has meant many different things over the course of human history. For instance, polygamous marriage was once very common (still is in some parts of the world). And for many centuries, marriage was primarily a financial arrangement and a way of ensuring inheritance rights. Women were essentially bought and sold. The modern concept of love as a basis for marriage is of relatively recent vintage. And civil marriage is a very different thing than religious marriage (which itself differs from religion to religion and culture to culture). The idea that there is some sort of platonic essence to marriage is just rubbish. Marriage was created by human beings and human beings can choose how they want to define it.