"I suppose I should ask you: how do you feel about couples who cannot (or do not want to) have children? Should they be allowed to marry? Or should they live their lives alone?"
I've known a number of couples who had no intention of having children but eventually did either because they had a change of heart about the matter, or it just happened and they decided to go for it. The biology is pretty strong there. As far as those folks who are unable to have children, I'd say that their union, though unable to produce children, at least symbolically reinforces and celebrates the societal model that typically does produce children. A homosexual union on the other hand is never able to produce children and moreoever directly challenges the traditional marriage model that does produce children. In any case, just because you aren't married doesn't mean you have to live alone. I had plenty of company before I was married. ;-)
"But I still feel that it excludes those who have every right to be married"
Anybody can get married, but there are restrictions on what or who you can marry. Do you think sisters and brothers should be allowed to marry as long as they agree to not have children? What about mothers and daughters or fathers and sons? Those would be homosexual unions with no risk of producing genetically weak offspring due to inbreeding.
"As far as those folks who are unable to have children, I'd say that their union, though unable to produce children, at least symbolically reinforces and celebrates the societal model that typically does produce children."
That, I can agree with. However, some members don't seem to think so. Those who cannot produce children should get some kind of cohabitation agreement rather than a marriage certificate (see post #30).
"But I still feel that it excludes those who have every right (i.e. legitimate marriage candidates, not siblings or other partners) to be married" - just for clarification.