Giorgos Keramidas, after reading an article about how
rm -rf / (i.e. accidentally deleting your operating system) is avoided by Sun, suggested on the firstname.lastname@example.org mailing list some changes to protect from that. An extensive discussion (bikeshed) ensued. See “Protection from the dreaded “rm -fr /” thread on the former link, if you are curious. It’s still not resolved.
On the other hand, this has been quickly fixed in DragonFly, without changing the basic function of rm. New installs will have this safer behavior by default, though the old unsafe setup can be restored if desired.