A former classmate from Yale recently told me “monogamy is kind of outdated” and not good for society. So I asked her what her background is and if she planned to marry. She said she comes from an affluent family and works at a well-known technology company. Yes, she personally intends to have a monogamous marriage — but quickly added that marriage shouldn’t have to be for everyone. She was raised by a traditional family. She planned on having a traditional family. But she maintained that traditional families are old-fashioned and society should “evolve” beyond them. What could explain this?...