So, why is it so bad to teach Google/Twitter/Facebook… which things interests you, when they use that data to find you more of those things?

Think about it this way: when you see something that enrages you, you are pretty likely to check it out. Click on it and the system learns that this is of interest to you. So in order to keep you engaged (make you see one more ad), you get more and more of the things you hate. The door you just heard slamming shut? That’s your mental health, leaving the building.

This whole “privacy does not matter, just pay with your data” nonsense is pretty much the reason why corporate social media platforms turned into the shitholes, they are.