This is the same argument people used to make for why it was fine for capabilities to be unrevocable--someone could have copied the data anyway (or whatever) so there was no point in revoking it. In reality, most of the time nobody but the host of a deleted item has access to the data, has a way to tie it to the originator, and has a motive to use it, especially without significant effort. Being able to delete things is a very important feature (not to mention a legal requirement in many countries!), and it's disturbing to me how many people seem to want to justify a world where every bit of data is saved, forever.