Shortening the rope (around RH's neck)

chattr +i on a directory will stop any files in the directory from being modified, from a quick test, but it won't stop subdirectories from being removed recursively by rm -r. So it's only really useful on files, but you don't want to make files in /bin unmodifiable -- they need to be be changed in system upgrades. So for the same reason you don't want to make /bin unmodifiable (it seems to prevent some modifications to files it contains, certainly at least removal and likely overwriting of all kinds).