Ignore the fact that your counterpart should want to show a different opinion on this matter. It also fails to demonstrate a real, good reason why anyone should be against gay marriage. He never talks about religion, which is one of the main reasons why marriage is given so much consideration in legal matters. Marriage is something held in high regard by religious cultures. Some people, not only atheists, but people who do not hold religion in high regard, sometimes argue that marriage is just a document that religious fanatics and old-fashioned people need to consolidate their union. If the marriage is solely for legal purposes, as implied throughout the story, there are other ways to legalize their union. There are wills, partnerships and powers of attorney that can help with legal matters if such a situation arises