Yes, I'm aware, and POSIX has many such bugs that make command input or output unavoidably ambiguous if certain unexpected characters are present that they didn't think to prohibit. A lot of the revisions that went into POSIX 2024 were aimed at fixing some of these, such as standardizing find -print0 and xargs -0. The fact that this one got overlooked doesn't mean it's a good idea to make the situation worse and harder for future POSIX revisions to address.
Allowing purely numeric usernames seems like a terrible idea to me, because it creates ambiguity between what's a username and what's a UID. It's common for tools like ls or ps to display a username when one is found and fall back to displaying a UID if it isn't, and similarly tools like chown will accept either a UID or a username and disambiguate based on whether it's numeric or not. Now suppose there's a numeric username that doesn't match its own UID, but does match some other user's UID. It doesn't take a lot of imagination to see how this would lead to vulnerabilities.
I retrained myself on Barchowski last year. Barchowski and its close cousin Getty-Dubay are italic rather than looped, and a lot easier to read for someone who only ever learned print.
Author of the essay here. I did a double take at seeing it posted here because I thought it was completely forgotten, nearly including by myself. I think the actual date of this essay is 2007 or maybe 2006, because I remember writing it from my university computer lab and I was class of '07. Anyway, there's certainly a lot of water under the bridge since then and the political composition of hackerdom today looks nothing like it did 15 years ago. With the growth of the FAANGs there are far more hackers today than there were then, and the younger ones are a lot more likely to be leftists than libertarians. Still, though, when I travel in libertarian circles it's pretty clear to me that hackers are overrepresented there, so I think the reverse remains true as well, even though it's not as dramatic or obvious as it was in the '00s.