Isn’t prohibiting same-sex couples from marrying just like prohibiting people from different races from marrying?
Not at all. When the courts struck down laws passed to prohibit interracial marriage, it did not change the basic social institution of marriage. It was still understood to be a union between a man and a woman, regardless of their races. Allowing same sex-individuals to marry, on the other hand, would radically redefine the fundamental and universal understanding of marriage over millennia of human history. No society in history has ever done this.