Rep. Jackie Speier introduced legislation today that would require the Federal Trade Commission to establish standards for a “Do Not Track” mechanism and require online data collectors to obey consumer opt-outs through such a tool.

As I’ll explain in more detail in my comments on the FTC’s privacy report (due next Friday), I’ve argued for the last two and half years  that user empowering users to make their own choices about online privacy is, in combination with education and enforcement of existing laws, the best way to start adddressing online privacy concerns. In principle, some kind of “Do Not Track” mechanism could be a valuable user empowerment tool.

But actually implementing “Do Not Track” without killing advertising won’t be easy. Just as consumers need to be empowered to make effective privacy choices, so too must publishers of ad-supported websites be able to make explicit today’s implicit quid pro quo : Users who opt-out of tracking might have to see more ads, pay for content and so on.

Government cannot design a “marketplace for privacy” from the top down, nor predict the costs of forcing an explicit quid pro quo . It would be sadly ironic—as Adam Thierer and I pointed out over a year ago—if the same FTC that has agonized so much about the future of journalism wound up killing advertising, the golden goose that has sustained free media in this country for centuries.

The market is evolving quickly here, with two very different “Do Not Track” tools debuting in Internet Explorer 9 and Firefox 4 just this week. Ultimately, it is the Internet’s existing standards-setting bodies, not Congress or the FTC, that have the expertise to resolve such differences and make a “Do Not Track” mechanism work for both consumers and publishers, as well as advertisers and ad networks.