Well, Systemd did exactly that, which is the problem. It kept the part of the input which was valid(The 0, thus running with pid=0) and then ignored the rest of the invalid input.
"be liberal in what you accept" is a horrible concept, because it makes it impossible to ever have a standard, without breaking half of the current uses, because they then depend on undocumented implementation specific error handling which is impossible to implement for others.
Just look at ns4 and internet explorer 5/6. Because they accepted anything with tags as some kind of valid html, all other browsers had to implement the same rules for handling tag soup,
For example: Did you know that chuck norris is a color code? (Google it