I'm not sure if you've ever listened to any Alan Watts lectures, but in one of them he spends some time telling a story about the different approaches of two music teachers, one who insists on playing the 'correct' notes and enforces this with a sharp thwack whenever a student gets the note wrong. The student ends up so afraid of playing the wrong thing that he can barely get through a few measures before giving up. The other teacher insists on finishing a piece without a break in the rhythm and enforces this by instructing the student to return to the beginning and playing the piece. This student spends many weeks playing through the piece until she has mastered it.

Teachers who tell students that they are tone deaf are usually a) impatient or b) of the belief that the 'wrong' note destroys a piece. In short ,they're short-sighted and have a very limited eye/ear for beauty. In shorter: Bad teachers turn willing students away.

Another little comment I have is role of courage in singing. Confidence in your ability to control your voice is the core of every singer's skill. Building that confidence is the first thing any teacher should do, because releasing a sustained series of notes into the environment has always been an act of courage, and without that courage we cannot engage with any song well enough for the listeners to let us continue.

The exclusion approach of music training I think is an outdated method from the the industrial revolution era, where unless you were a prodigy, you were better off ('more useful') in the workhouse.

However, these days, with all the great research done on teaching in general, the old approach to teaching music is fast fading away, as evidenced by the fact that music teachers like you exist and call the bst out for what it is. :)