Debate evaporates in the face of a real attack, as was seen this year when some British airports introduced compulsory "electronic strip-search" scanners following the Christmas underpants plot.
Skeptics were dismayed several years ago when a group of societies including the American Medical Association tried to end the debate by issuing a joint statement.
In the past couple of weeks a quarrel has illustrated the value to advertisers of such fine-grained information: Should advertisers assume that people are happy to be tracked and sent behavioural ads?