Ask Slashdot: How Is It Even Legal For Websites To Gather And Sell Users' Data?

Long-time Slashdot reader dryriver sees it like this:

Lets say that I follow a person named John D. around for days without permission, make note of what John D. does and where he buys with timestamps accurate to the second without John D. knowing it is happening, analyze what kind of personality traits John D. has, enter that data into an electronic database where it is stored forever, and also make the data purchaseable to any third party who is interested.

Would I be breaking the law if John D. has not given me explicit permission to do this? Very likely. If this is the case for 'meatspace data gathering', how can websites justify gathering information about visitors, and selling that information to third parties?

How would you answer this question? Attempt your own best explantions in the comments. How is your country balancing the need for online privacy with actual laws governing what can and can't be collected?

How is it even legal for web sites to gather and sell users' data?

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