In the context of VPNs for example. Some VPNs store and provide information about what sites you go to third parties. Third parties analyze it and figure out what adds to show you. Hmm… then let them show me those adds they want to show me. I do hate adds as a whole and use an add blocker, thus. But I couldn’t care less what particular type of adds they show me, they are still adds.
Someone knows what sites I go, what then. If someone curiously inquired me on this type of information I’d tell them without giving a second thought. Incomparably larger amount of data I put out just by making comments and posts.
Although my anecdote ended with additional data collection, the scary part is the manipulation of action. You might think that, as an example, they see you browsing a pokemon website and therefore show you more pokemon ads, something that coule be mutually beneficial. What you should be worried about, is something like based on your browsing behaviour they figure out how to manipulate your political action, or figure out your state of mental well-being and manipulate it. There is especially horror cases here when this is algorithm driven instead of being pushed by humans. One could imagine ,and I want to preface this by saying I’m not aware of this ever having happened, a machine learning algorithm relating signs of some mental illnesses with an uptick in firearm sales, and then increasing advertising of firearms to those people. You could imagine this driving things like an increased suicide rate.
There are many more other outlets for propaganda. Their effectiveness are hard to measure as well as the effectiveness of ads. Figuring out how to manipulate is philosophically impossible. How would you train an AI if you don’t know if your actions led to success or not. Mental conditions are themselves poorly understood and defined. And we only have superficial web browsing data at our disposal.