"Let Truth and Falsehood grapple; who ever knew Truth put to the worse, in a free and open encounter?" asked John Milton in Areopagitica, his rousing defence of a free press, in 1644. But in an era when a blog can be set up with a few clicks, not everyone agrees that more voices and more choices improve the quality of debate. Cass Sunstein, a Harvard law professor, has argued that by allowing people to retreat into "information cocoons" or "echo chambers" in which they hear only views they agree with, the blogosphere fosters polarisation—a fear widely shared by politicians. Forbes once called blogs "the prized platform of an online lynch mob spouting liberty but spewing lies, libel and invective."