So what? I am so weary of deflecting this ridiculous argument. Since marriage is defined as the union of a man and a woman, then people on their death beds and infertile men and women are welcome to get marriage licenses. OK?
The reason why marriage is defined as a union of a man and a woman is that men and women in general do procreate. Marriage is important to protect the family structure, which in the vast majority of cases involve mothers and fathers.
Allowing same-sex couples the right to marry in no way changes other people's ability to marry, and raise families.
"Since marriage is defined as the union of a man and a woman"
Guess what?
That definition is about to change.