DEAR MISS MANNERS: At long last -- I disagree with you! Ha!
It is about your contention that the audience's response after a professional show is not intended to thank the performers, but to show how they feel about the performance -- positive, neutral or even negative.
I am myself a stage artist and know life from both sides of the footlights. If the art presented has been pursued with any sort of seriousness, audience members are witnessing many hundreds of hours of good, honest effort brought to this moment of truth, with all it costs in so publicly exposing one's greatest strivings.
This must be respected. It is never OK to boo, it is never OK to "critique" the performance to the artist's face right afterward.
Hate the show? Just leave. Think it could have been better? Wait until the next day, when the artist has rested and you have slept on your own perceptions, and then write a note to them, or seek them out for a cup of coffee.
Praise what was good -- and there is always something! -- before vouchsafing your thoughts on "what could have been better." The occasion of artists bringing the most precious thing they have to offer is NEVER the occasion to engage in cheap, self-congratulatory criticism. It is certainly not the place to engage in aesthetic pillow fights with one's fellow audience members.
GENTLE READER: Does an aesthetic pillow fight require matching pillows?
While Miss Manners does not applaud cheap or self-congratulatory behavior of any kind, she is perplexed by your logic. The refrigerator that you bought online also represents hundreds of hours of good, honest effort. When it breaks in the first month after installation, do you seek out a customer service representative for a cup of coffee, praising the fact that the refrigerator light continued to work so that you were able to see how much of your food had been ruined?
That the professional performer is uniquely "exposed" strikes Miss Manners as neither true nor flattering. The actor can blame the director, the CEO can blame subcontractors or the government, and the politician can blame the media -- admittedly none with much success. But the actor who argues that his performances are merely a public airing of his own painful secrets denies the craft, hard work, professionalism and experience.