“I’m done with my grandfather,” a friend confided in me after a recent family gathering. “He compulsively talks about how George Soros is to blame for everything—and then refuses to recognize any evidence to the contrary,” she said. “He has his talking points, and there’s no changing his mind. It’s not even worth having a conversation.” In our polarized moment, we sometimes struggle to fulfill basic social or professional obligations with family, friends and co-workers who hold views we find objectionable. But we ought not cut people off without thinking carefully the consequences. It’s not just that we risk losing important relationships. People whose ideological or political opinions we oppose may still have something to offer. Cutting them off leaves us both intellectually and emotionally poorer. Most of us have stories like the one my friend told me. And while the details differ, they all go to a central question: What is the unspoken social contract that governs how we discuss ideas? At what point do we no longer have to listen to what another …