Shazard - from what I understand of your argument is that since gay people cannot reproduce, they should be denied the right to marry. However, as I'm sure you are aware, there are plenty of straight couples, married and unmarried, who do not have children, either because they cannot or because they simply don't want children. Should we then deny THEM the right to marry? Marriage is far more than just children. It is about sharing legal rights and responsibilities, independent of reproduction.
I don't really understand your argument about paying straight couples to have more children. How does gay marriage do anything to change whether or not people want children? Will it suddently make straight people not reproduce?
There are plenty of gay couples who have adopted children and are raising them just as a straight couple, or as single straight parents. However, many states (in the USA) don't recognize gay couples, so the legal rights to those children are denied to those couples. If the legally-adopting parent dies, the partner in the relationship runs the risk of losing custody because his or her rights are explicitly denied.
So far the arguments against gay marriage fall flat.