I don't think the issue is being professional or not. If the author's goal is to convince people who work on Hugo to improve the docs, then it's best to avoid triggering a defensive emotional reaction. The title as it stands will likely trigger hurt feelings, which is usually followed by being defensive or ignoring the substance of the criticism. That's simply unproductive.

You're probably right, but I think not being a jerk should trump HN upvotes.

This makes me think of the old programmer joke that's something like, "There's no documentation. If it was hard to write, it should be hard to understand."

In project like Hugo that has no "user interface" to speak of, tools for which you can't reasonably be expected to just look at the UI screens and figure things out if they're nicely done because there are no UI screens to look at, the documentation is the user interface. Full stop.

The article lays out exactly what its author doesn't like about the documentation and makes suggestions for improvement. The "your documentation sucks" title is the harshest thing about it, and if it was truly a rant I could see getting prickly about it, but it absolutely is not. This is constructive criticism. And that's just as important for an open source project as it is for any other project.

I get bristling at the "if you can't stand having your suggestions torn apart, then don't contribute to open source" weird macho mindset some projects have historically have. Yes, it's toxic. But "if your suggestion is not sufficiently deferential, away with you" goes too far in the other direction.