I think 'rm -rf /' shouldn't work and there should be special command instead of 'rm -rf /', something like rmrfhell, which would ask you three times if you sure and will tell you about pain and tears of other people who ran it.
Most versions have --preserve-root (fail if the target is /) on by default, so you have to use --no-preserve-root , although rm -rf /* will still work.
