The point is that ACLU members did not choose to give up their privacy:
"The group's new data collection practices were implemented without the board's approval or knowledge and were in violation of the ACLU's privacy policy at the time, according to Michael Meyers, vice president of the organization and a frequent internal critic. He said he had learned about the new research by accident Nov. 7 during a meeting of the committee that is organizing the group's Biennial Conference in July.
He objected to the practices, and the next day, the privacy policy on the group's Web site was changed. "They took out all the language that would show that they were violating their own policy," Meyers said. "In doing so, they sanctified their procedure while still keeping it secret."
Quoted from: http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2004/12/18/MNGCOADSEL1.DTL This site does not require registration, I believe.
Another point - if it had been any other company or organization that had engaged in this data collection, the ACLU would be suing them out of existence with a zeal that would make their jihad against the Boy Scouts look laid back.