The problem with this idea is that different consumers might have a different subset of what they accept and correct.

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.