After reading some more comments, I think I came up with a good analogy to explain this issue, and I wanted to share.
Think of websites like a bar that also has an open mic.
Now, when I go to a bar, I don't want to have to give the bouncers and staff my full name as well as my address. I also wouldn't want them to know that I just came, for example, from a store where I was looking for a vacuum, and then have them warn a vacuum seller about it. A vacuum seller who is then going to sit next to me, while I'm trying to have a drink, and show me a pamphlet regarding the "amazing vacuum" he has for sale.
Ideally, I can also look for a bar that will allow me to come in costumed and not show my face. Or I could ask the bar to delete footage of me at some point, and to not store my ID if I do have to show it to a bouncer at the entrance.
All of that is relatively feasible and within the realm of reason; and all of that are things that privacy advocates might advocate for.
However, what is not feasible, or within the realm of reason, or what privacy advocates tend to advocate for, is the ability for me to willingly go up on stage, say something on the mic which I immediately regret, and then ask everyone present to forget it ever happened and delete any footage they might have of it. No reasonable person would ask for something like that, because it is not a reasonable request.
That is how regular websites work. With federated websites, that becomes enhanced; it's like if the bar you're in has a camera pointed at the microphone, and transmits both video and audio directly into several other bars. So when you go up to that mic, you better make sure you're okay with what you are saying being made public and available to anyone.