Johannes, There isn't one - they're talking out of their ass.
They're just making noise and emotionally distressed to discover that this is how the #Fediverse currently works, and always has worked - and it's not just the #ActivityPub portions of the Fediverse, or even the Fediverse - it's the entire #Internet...
"If you affect a public post, you have no expectation of privacy".
For those who still feel some sense of having been offended, I welcome them to unplug their computers and toss their iPhones and Androids into the trash. That's really their only option, and they'll come to that realization some day, maybe, and it is of no consequence for anyone else in the world if they don't.