1. It Is Not Marriage
Calling something marriage does not make it marriage. Marriage has always been a covenant between a man and a woman which is by its nature ordered toward the procreation and education of children and the unity and wellbeing of the spouses.
The promoters of same-sex “marriage” propose something entirely different. They propose the union between two men or two women. This denies the self-evident biological, physiological, and psychological differences between men and women which find their complementarity in marriage. It also denies the specific primary purpose of marriage: the perpetuation of the human race and the raising of children.
Two entirely different things cannot be considered the same thing.