If a tool unconditionally produces diagnostics on standard error, whether there is an exceptional situation or not, I consider that poor behavior, contrary to t

If a tool unconditionally produces diagnostics on standard error, whether there is an exceptional situation or not, I consider that poor behavior, contrary to the quiet tool philosophy from Unix. Standard error is special output that the user should be able to somehow see (e.g. on a terminal) even if the regular output is redirected (as you note above). That doesn't mean standard error is above the quiet tool guideline.