• by Wendy Davis , Staff Writer @wendyndavis, July 1, 2011

This week's Senate Commerce Committee hearing about online privacy has led a host of observers to weigh in on the pros and cons of a universal do-not-track mechanism that would allow consumers to easily avoid all online tracking.

The U.S. Chamber of Commerce, Interactive Advertising Bureau and a slew of other ad and business associations are urging lawmakers to support continued self-regulation. They argue that the umbrella group Digital Advertising Alliance already allows people to opt out from receiving ads targeted based on tracking data; additionally, they say, people can control cookies through their browser settings.

"Any government restriction on the ability of companies to gain revenue from advertising would result in less free or subsidized content being made available to users and would inhibit innovative start-ups," they argue in a letter sent to lawmakers this week.

Privacy groups and consumer advocates, meanwhile, argue that "it is obvious that technology has outpaced the law."

"There is still nothing comparable to the successful Do Not Call program to protect consumers from unwanted advertising and profiling by Internet firms," groups including the ACLU, Center for Digital Democracy and Electronic Frontier Foundation say in a letter sent to lawmakers this morning. "Consumers have no meaningful ability to limit the use of their personal information that they provide to companies online."

In reality both advocates and opponents appear to be overstating the nature of the proposal on the table. The concept of a universal do-not-track mechanism isn't radically different from the current self-regulatory program, which offers users links from which they can opt out of behavioral targeting by the major ad networks. The single biggest difference appears to be that ad networks in the industry's program need not stop tracking users who opt out; rather, they only need to stop serving them targeted ads. Many ad networks, however, do stop tracking users who opt out.

Other than that, the distinction between the opt-out links and a single do-not-track mechanism is that a browser-based do-not-track will probably persist longer than opt-out cookies, given that many users routinely delete all cookies.

The proportion of users who opt out of behavioral targeting has always been very small. Given that users aren't clicking on opt-out links in any large numbers, there's little reason to think that many will activate do-not-track headers.

And, while privacy advocates say that the industry has nothing equivalent to a do-not-call registry, no proposals being discussed right now would change that. Consumers who sign up for the do-not-call registry can avoid all telemarketing calls. But people who say they don't want to be tracked will still receive ads; they just won't be targeted based on users' Web-surfing history.