But the question confused me. Why would a valuable piece of social progress close a literary door? Nobody thought women would no longer be a good subject for fiction once they got the vote. Nobody argues that African-American literature ended when Obama was elected. I soon developed a handy response: “Oh, no — gay marriage is going to give us a whole new subject to write about.” But since then I’ve been thinking it over more closely, wondering just how same-sex marriage might affect literature, about what could change and what may have been there all along.