Mutual care. If you are married (or in a civil union or domestic partnership or whatever separate-but-equal code word people want to use to grant gay people almost-but-not-equal rights), you engage in mutual care for one another. You look after each other when sick, you cover for each other's temporary financial shortcomings (when they lose a job for instance). You provide a whole lot of care that if you weren't together would be something that society would have to provide, especially in older age.
Take my paternal grandparents. When my grandmother was still alive, the two of them happily lived together and cared for one another even though my grandfather was at that point experiencing the early onset of dementia.
When she died, my grandfather had to go into residential care, paid for partly by their pension, partly by my parents and uncles, and partly through the subsidy that the state provide for elderly people going into care homes.
The more people who are able to live together in a mutually caring relationship like a long-term marriage, the less people need to go into care homes meaning the less subsidy needs to go into that kind of care for the elderly.
Marriage has a societal benefit in promoting that kind of mutual care, regardless of the gender of the partners and regardless of whether you have kids (and, hell, same-sex couples can and do have kids, so that's a shit argument anyway).
Could you set up another system to provide that kind of benefit? Sure. But this is the system we have and it should be available to long-term gay couples as it is for straight couples.
Take my paternal grandparents. When my grandmother was still alive, the two of them happily lived together and cared for one another even though my grandfather was at that point experiencing the early onset of dementia.
When she died, my grandfather had to go into residential care, paid for partly by their pension, partly by my parents and uncles, and partly through the subsidy that the state provide for elderly people going into care homes.
The more people who are able to live together in a mutually caring relationship like a long-term marriage, the less people need to go into care homes meaning the less subsidy needs to go into that kind of care for the elderly.
Marriage has a societal benefit in promoting that kind of mutual care, regardless of the gender of the partners and regardless of whether you have kids (and, hell, same-sex couples can and do have kids, so that's a shit argument anyway).
Could you set up another system to provide that kind of benefit? Sure. But this is the system we have and it should be available to long-term gay couples as it is for straight couples.