I think the alternative being suggested is that rm shouldn't accept a string that magically can reference anything in the filesystem...

In our capability-based shell scripting language Shill (shill-lang.org) for example, you could prevent this sort of bug by giving the script a capability for just the diaspora_home directory, and deriving the child directories from that capability. (Of course, you still need to make sure you pass in the right directory in the first place.)