I oppose same sex marriage as much as abortion. Homosexuality is wrong. Marriage is between a man and a woman. By the way, sperm banks are another immoral development in our culture. Becoming pregnant in this way is a violation of the unitive and procreative purpose of sexual intercourse. In answer to your question, an infertile couple does not violate the purpose of sex because they cannot have children. God decides who will have children. Regardless of the fertility of the couple; sex and marriage was designed to unite a male and female within marriage. Homosexuals will never under any circumstances be able to fulfill this purpose. It doesn’t matter if they use 200 spem banks and have 100 children, buy a house in the suburbs and have 10 Golden Retrievers; the relationship is still immoral, gravely evil, and a violation of natural law!