I think, ultimately, this information HAS to be out there - for singers who don't know, for teachers who don't know - and told however it has to be told. It shouldn't be about emotion - it has to be about the etiquette and expectation.
Sometimes people need to be told point blank what is being seen so they can make the adjustment. I've seen it happen at masterclasses with very well-known divas who have said to participants "you aren't dressed appropriately, you must sit down". I would much rather a singer learn that etiquette on a forum, from a teacher or coach than in a truly public space that singles her/him out.