But it is suggesting us to make a purchase based on our browsing history. Indeed, they don't really do anything more than that -- but they did take information from us without us giving a consent for it.
Think of that as if you were a regular customer at a store with a regular worker.
You buy the same shit all the time, the worker eventually starts recognising you after your 10th time of getting that said same shit.
One day you find all your same shit packed nicely in a few bags and get a nice friendly wave from the worker.
Why? Cause he knew what you were there for and decided to do it for you.
Obviously it's different for web browsing, but the concept is the same.
The worker isn't invading your privacy because he picked up your routine.
Internet marketing tactics aren't infringing that either.
Though getting ad block saves you the hassle of seeing them.
However, the 'harmless' prank on facebook is in fact infringing privacy.
If your intent was so that you could use your stuff and only you, then someone else using it would be infringing that.
(ie unless your friend told them they could write that, they shouldn't have done it. Period)