You'll also find few protocol designers designing anything as robust as the old protocols. :)
I mean, don't go out of your way to under specify input. But relatively nobody is going back to the heavy schema of xml over simple json. Even if they probably should.
I feel this is an anti fragile position. Try not to encourage poor input. But more importantly, be resilient to it. Not dismissive of it.
Robust as the old protocols? The early TCP protocols are very much underspecified. Maybe you have something else in mind.
Fair. I view them as what they grew into. Not as what they were initially designed as. Probably not a straight forward comparison.
I've just gotten weary of so many replacement protocols that get dreamed up and go nowhere. Often because they didn't actually learn all of the lessons from predecessors.
If some of those become dominant, produces might start depending on that behavior and it becomes a de facto standard. This is literally what has happened to HTML, but holds true for many other Internet protocols.
If you're looking for some external reading, I found at least this:
* https://tools.ietf.org/html/draft-thomson-postel-was-wrong
I think you'll find few protocol designers arguing _for_ the robustness principle these days.