Second, dealing with piracy is the responsibility of Dropbox. It’s not the problem of an innocent hacker who wrote some useful code that could benefit legitimate users and advocates the use of his software for “sharing photos, videos, public datasets, git-like source control, or even as building block for wiki-like distributed databases."
Could someone give me 1 example of a use case here? The only reason I can think of to share the hash of a file instead of a direct link, is because it's an illegal file, and you don't want to link straight to it. Why else would you go through the effort of hashing all 4mb blocks of the file, and sharing those elsewhere?
Of course, this is a dangerous gray legal area, but I think it's fair to say that the only reason to use this is because of illegal files. Also, they didn't take legal action (which wouldn't be right, as no one has been proven of doing illegal stuff), they just asked nicely, so it seems. Dropbox is right to act on this, as it could potentially ruin their platform.