The last time I saw Mark Zuckerberg was in the summer of 2017, several months before the Cambridge Analytica scandal broke. We met at Facebook’s Menlo Park, Calif., office and drove to his house, in a quiet, leafy neighborhood. We spent an hour or two together while his toddler daughter cruised around. We talked politics mostly, a little about Facebook, a bit about our families. When the shadows grew long, I had to head out. I hugged his wife, Priscilla, and said goodbye to Mark.

Since then, Mark’s personal reputation and the reputation of Facebook have taken a nose-dive. The company’s mistakes — the sloppy privacy practices that dropped tens of millions of users’ data into a political consulting firm’s lap; the slow response to Russian agents, violent rhetoric and fake news; and the unbounded drive to capture ever more of our time and attention — dominate the headlines. It’s been 15 years since I co-founded Facebook at Harvard, and I haven’t worked at the company in a decade. But I feel a sense of anger and responsibility.