If you like removing important files, or recovering from damaged *nix systems, be sure to read also the classic recovery story from 1986:
http://www.ee.ryerson.ca/~elf/hack/recovery.html
"I leant over to another terminal, already logged in, and typed
grep 147 /etc/passwd
only to receive the response
/etc/passwd: No such file or directory.
Instantly, I guessed that something was amiss. This was confirmed when in response to
ls /etc
I got
ls: not found.
"
http://dan.langille.org/2015/08/29/deleting-files-from-usr-breaking-your-system-then-recovering
As amazing as the story is, the moral of the story is rm -rf / is broken; even as root allowing this makes no sense.
I think more recent GNU versions of rm are more to your liking. See
http://www.gnu.org/software/coreutils/manual/html_node/Treating-_002f-specially.html#Treating-_002f-specially
Although… it wouldn’t have helped the chap who removed a bunch of subdirs from /usr