I am not saying that this is not a bug, just that this isn't the problem that the author is making. If you have local access, you probably can do other things if your only objective is to do a DoS.
"If you think systemd doesn't need privilege separation because it only parses messages from local users, keep in mind that in the Internet era, local attacks tend to acquire remote vectors. Consider Shellshock, or the presentation at this year's systemd conference which is titled "Talking to systemd from a Web Browser.""