Hindsight is always 20/20 and norms change quickly on the internet; we could say equally critical things about Telnet and FTP.
I agree that P3P clearly needs some rethinking to stay relevant. Especially now that the cat's out of the bag on how to bypass it. (Microsoft's immediate response is to set up yet another blacklist system... some cultures just never change.)
For everyone's entertainment, the OP's comments linked to an amusing satire of P3P called P5P, or the "Pretty Please Platform for Participating Publishers." This is possibly the best collection of protocol tokens I have seen since RFC 2324.