It is, for example, a fact that history and tradition have until recent years, limited marriage to one man and one woman. It is also a fact that history and tradition have, until recent decades, encouraged the oppression and enslavement of women, people of color, people with disabilities, etc. They took their arguments to the streets, to the legislature and to the courts. People, impassioned by an idea whose time has come, use whatever means are necessary to reach other people who are resistant to the idea. But, thankfully, times change.
Marriage today is more about the human desire for committed intimacy that is companionship.
The marriage ceremony is a formal acknowledgment that two persons care so much about each other that they intend to commit their lives to practicing that care. Maybe they will have children, maybe not. Maybe the woman will take the man's name, maybe not. Maybe they will live together in the same house, sleeping in the same bed for the rest of their lives, maybe not. Maybe they will, eventually, divorce.