China operates the world’s most elaborate and opaque system of Internet censorship. But Congress, under pressure to take action against the theft of intellectual property, is considering misguided legislation that would strengthen China’s Great Firewall and even bring major features of it to America. The legislation — the Protect IP Act, which has been introduced in the Senate, and a House version known as the Stop Online Piracy Act — have an impressive array of well-financed backers, including the United States Chamber of Commerce, the Motion Picture Association of America, the American Federation of Musicians, the Directors Guild of America,...