Marriage used to be a white man marrying a white woman. Black people, being slaves, couldn't legally marry each other, and a white person couldn't legally marry a black person.
Then black people could legally marry, but still couldn't marry white people.
Then black people could marry white people.
Soon, people will be able to marry someone of the same sex.
Someday, people will be able to marry multiple people. And I have no problem with that, either, as long as they're consenting adults.
But do you know what will never happen? People will never be able to marry children or animals. Because children and animals cannot consent.
What is it about consent you people don't get?