Comment by AnthonyMouse

> On Android, each of those three apps would ask you for file system permissions on first launch. Your choices are "full access to user files", "limited access" (usually one directory and all its sub-directories), "full access, but only this time", and "no access".

Which isn't completely useless, but in most cases the only thing you really want is "full access" or "I don't actually trust this thing" -- and most users aren't going to comprehend the difference between more fine-grained alternatives anyway -- and then you're basically looking at the distinction between normal trusted apps and something you run in a container.

> Also, apps can pretty much never access each others config/keys/etc files - which they never should.

And that's the problem, because the backup app is supposed to be able to back up everything, a malware scanner can't have potentially malicious apps hiding something from it, etc.