Given that far less total of gay couples by the very nature of their unions are going to be raising children within the relationship the society seems to have far less of an interest in promoting stable homosexual unions then hetrosexual unions.
Do you have evidence that gay or lesbian married couples will be raising fewer children than heterosexual married couples? It seems a very difficult thing to measure without first eliminating the discriminatory practices in place. Practices at this point, which serve as social and legal hurdles for these couples to adopt.
I know of many loving and well functioning same-sex couples who are raising children. Regardless, where would you rather children be? In foster care or in the family of a committed (through marriage) two parent family?
My parents are Catholic. They would like to see fewer abortions in society, being intelligent observers of societies and the Church over the last 1000 years, they realize the folly of theocracy. So how do my parents help society?
They adopt 3 children and have served as foster parents for over 20 different children over the last 10 years.
Frankly, it leaves me disgusted to hear of anyone attempting to limit the number of available couples who can adopt children out of the foster system. Do you realize that if just one couple from each church in this country adopted just one child, there would be no children in foster care?
I don't know if you are religious, but if you are I would suggest spending less energy worrying about who marries whom, and more worrying about children having homes.