You don't need a marriage license to live with someone, to have the security of a home, to rear any number of children, to have years of companionship; it's not illegal, but the moment you want to screw somebody, you have to get a license from the state to use your genital organs -or run the risk of being charged with any number of crimes carrying sentences up to and including death. So sex is really the only sensible reason for getting married.