One of the so called arguments against same sex marriage is that it "redefines" marriage. Republican presidential candidate Rick Santorum stated that same sex marriage would be like calling a napkin, a paper towel.
Marriage to him is defined as man and woman, only. O.K. this is a logical fallacy. A paper towel is close to a napkin, but there are slight differences in size and slightly different purposes. They have slightly different attributes. But, they were both created by human beings to serve the purposes of human beings.
Marriage was created by human beings. It is something that is wholely and completely a human invention, and as a human invention the definition of it depends on how we define it. Marriage would not exist without human beings, while something such as trees or cats would of course exist without humans. A tree cannot be a cat, because we didn't create those things, but we created marriage.
Our ancestors had a definition of marriage slightly different than our own, of course. They defined it as women being property, with few or any rights. That has evolved of course as women gained more rights within marriage.
Society progressed, just as it is now with growing acceptance of same sex marriage. Now, are we going to state it was wrong for women to gain greater status within marriage, because it changed, to some degree at least, the definition of marriage as it existed at that time? Of course not.