The reason so many people have against allowing homosexuals to marry is that they feel marriage is about having and raising kids.
It would seem to me that people who feel this way should also be against allowing older people from marrying (such as ones whose kids are already grown, or who had no kids in the first place).
They should also be against allowing infertile people to marry.
I will l not accept the argument here that the person's infertility can be cured - let's assume it cannot, or they are infertile because they had surgery done and don't want kids.
I point out as well that just because a person is homosexual doesn't mean they cannot conceive a child through other means.
Being homosexual doesn't mean a person doesn't want kids at some point.