To the point that it does not make users any more vulnerable to intrusive government actions, as you put it -- in practice, that's not going to be true.
Let's say right now Agent Bob or RIAA layer Cindy decides they want to know everyone in the country who has a copy of a file. There's no practical way for them to do that. But now, they can upload target.iso to dropbox, see that it uploads instantly, and all they have to do is get a court order to compel Dropbox to tell them all the other users who have that file.
Every user that has that file is now exposed. Dropbox is now a single point of failure for every user's privacy, and vulnerable to attacks from any legal court order -- and we've seen what can happen with the abuse of prosecutorial and judicial power. Copyright infringement's the obvious case, but when you start to consider how this ability to fish for files could be abused, and how tempting it'll be for people try to abuse it, it seems more serious than I think you're considering.
Let's say right now Agent Bob or RIAA layer Cindy decides they want to know everyone in the country who has a copy of a file. There's no practical way for them to do that. But now, they can upload target.iso to dropbox, see that it uploads instantly, and all they have to do is get a court order to compel Dropbox to tell them all the other users who have that file.
Every user that has that file is now exposed. Dropbox is now a single point of failure for every user's privacy, and vulnerable to attacks from any legal court order -- and we've seen what can happen with the abuse of prosecutorial and judicial power. Copyright infringement's the obvious case, but when you start to consider how this ability to fish for files could be abused, and how tempting it'll be for people try to abuse it, it seems more serious than I think you're considering.