[rsanders]

The kernel does quite a lot of work to prevent user-space programs from doing stupid stuff to each other, or to at least ameliorate the impact of such stupidity. One of the Unix philosophies has always been to prevent a runaway program from rendering the system inoperable.

systemd has apparently elevated itself somewhat above the typical "user space" level, but it's still not a bad idea to harden the interface between systemd and the kernel where possible.