But what is unlikely to happen is that they are unlikely to go out to every person on the fediverse and send them an informed consent letter that says "do you consent to us processing dislikes for your posts on our services?"
Why? Because it is part of the ecosystem here, even if it is not a widely used part, and they are behaving basically like a typical server in this regard!
This is where you have an implied or assumed consent and _no one thinks this is weird_.
It's an opt-out system
4/
Further, I don't like it, but it's definitely _in the ActivityPub spec_ that things sent to servers may end up being sent to _every shared inbox that the server knows about_ ( https://www.w3.org/TR/activitypub/#shared-inbox-delivery ).
Do servers need to seek your individualized consent for each server that they forward it to? Or can they assume consent because you are using a mastodon service, have marked your message as #'Public, and because the spec says that they can?
There's no one right answer here.
5/
Further, I don't like it, but it's definitely _in the ActivityPub spec_ that things sent to servers may end up being sent to _every shared inbox that the server knows about_ ( https://www.w3.org/TR/activitypub/#shared-inbox-delivery ).
Do servers need to seek your individualized consent for each server that they forward it to? Or can they assume consent because you are using a mastodon service, have marked your message as #'Public, and because the spec says that they can?