> The state has a vested interest in procreation (i.e.: creation of new citizens & taxpayers as others die off), so takes an interest in "marriage" as a means for facilitating the most efficient & effective means of promoting procreation, doing so by giving special benefits in return for parents taking on special obligations. Expanding the beneficiaries of those benefits to those to whom there is absolutely no chance (to the point of the notion being preposterous based on just 2 literal bits of information) of procreation is giving benefits to those whom will give nothing back in return.

So, you think marriage shouldn't be available for straight people who are both infertile?

You ignore the important role that marriage plays in mutual care. Marriage gives legal backing and support (in the form of certain tax and other financial and non-financial benefits) to a reasonably large set of people in long-term care relationships. Those people who care for each other aren't going to be needing as much support from the public purse to care for them when they get older, because they care for each other.

My dear old grandparents cared for each other when they were old - when my grandma died, my grandfather had to go into a residential care home. But because they were together, they provided care for each other that prevented both from needing that social care for a long time. Long term gay couples will give something back in return: caring for each other, providing health and wellness benefits that would otherwise be something that the welfare state may need to provide.

The state has a strong vested interest in people caring for each other. Here in Britain, the support given to parenting are done for parenting regardless of marital status in the form of child benefit payments.