And if you were using paper Alice could photocopy the document and hand it Bob. The answer to this problem is Alice needs to know who this information can and cannot be shared with. If she isn't capable of that these permissions won't help anyways.
There is a difference between the effort of photocopying individual documents and sending them along one by one, and getting them automatically synced to my competitors.
Just because an employee can copy out all files does not make it acceptable for software to re-share out confidential data without so much as sending a notification to the owner. There's no such thing as perfect security, but raising the bar and making malicious behavior more difficult is not a bad thing, especially when it improves the UX.
