When online ad executives talk about the prospect of regulating behavioral targeting, one of the first things they argue is that Washington shouldn't get involved without proof of harm. And in the past, the Federal Trade Commission has largely focused attention on business practices that resulted in some sort of tangible harm. But these days, the position that behavioral targeting can pose a threat regardless of whether it causes a concrete, quantifiable harm seems to be gaining favor in Washington.

This summer, Amazon caused an uproar by deleting copies of George Orwell books from users' Kindles due to a licensing problem.