I fear for the world the Internet is creating. Before the advent of the web, if you wanted to sustain a belief in far-fetched ideas, you had to go out into the desert, or live on a compound in the mountains, or move from one badly furnished room to another in a series of safe houses. Physical reality—the discomfort and difficulty of abandoning one’s normal life—put a natural break on the formation of cults, separatist colonies, underground groups, apocalyptic churches, and extreme political parties. But now, without leaving home, from the comfort of your easy chair, you can divorce yourself from the consensus on what constitutes “truth.” Each person can live in a private thought bubble, reading only those websites that reinforce his or her desired beliefs, joining only those online groups that give sustenance when the believer’s courage flags.