what's sold in the free market of ideas

Alain de Botton finds himself having a little more time for Socrates' defence of cultural censorship as it appears in Plato's Republic. The argument there is that bad ideas can ruin your life.

'It won't escape the notice of any inhabitant of a large city that the thoughts which greet us in public places are overwhelmingly interested in directing our attention to the advantages of consuming deodorants, airline flights and blockbuster films. If we really lived in a free market of ideas, we should expect that we would occasionally hear a public defence of kindness or a paean to the wise aphorisms of Marcus Aurelius, but we don't, for the obvious reason that few gentle Buddhists or stalwart Stoics have the £100,000 necessary to start an effective ad campaign.'