Alternatively, if, like he says in the comments of that bug, he really means that SystemD shouldn't support systems that allow such usernames, then he should ensure SystemD won't run on such systems.
Silently doing the wrong thing is not a good thing, especially when "doing the wrong thing" is running stuff as root that wasn't supposed to run as root.
Silently doing the wrong thing is not a good thing, especially when "doing the wrong thing" is running stuff as root that wasn't supposed to run as root.