To stop a deletion, you would have to get everyone who has a part of the file on their computer to preserve it. Since there are a large number of unrelated part

To stop a deletion, you would have to get everyone who has a part of the file on their computer to preserve it. Since there are a large number of unrelated parties running these computers, and the uploader can choose which to use when uploading, an attacker trying to prevent deletion will have quite a lot of fun convincing all these people to cooperate. I was skeptical at first too. But it might just work in practice.