Thanks for the link to the previous discussion of "ultracrepidarian," Audiendus.
According to Wikipedia:
"The English essayist William Hazlitt most likely coined the term "Ultracrepidarian" as first used publicly in a ferocious letter to William Gifford, the editor of The Quarterly Review:
1819 HAZLITT Letter to W. Gifford Wks. 1902 I. 368 You have been well called an Ultra-Crepidarian critic. (Oxford English Dictionary 2nd ed.)
A related English proverb is "A cobbler should stick to his last" (a last being the wooden pattern used to mould the shoe)."
Quoting Wikipedia raises the issue of whether contributors to Wikipedia ultracrepidate.
Personally, I find the saying smacks of smug authoritarianism. Yes, generally it is correct that people should speak within their expertise, but sometimes those speaking outside their apparent competence are correct, and the "authorities" are wrong, take Alfred Wegener for instance. Though schooled in astronomy, in the face of scathing criticism from titans in the field of geology he correctly theorized that the present continents had moved ("drifted") and were once part of of a larger supercontinent, Pangaea. Eventually his ideas were refined into the modern theory of plate tectonics. Time would vindicate Wegener and leave the so-called experts with egg of their faces. His ultracrepidarian story is here http://www.ucmp.berkeley.edu/history/wegener.html
Perhaps the rejoinder to ne sutor ultra crepidam
is even Homer sometimes nods