I personally find this odd but I do understand. There is something very personal about singing and expecting a beginner to just "go for it" right from the off is unlikely. It's far easier to learn to play the violin and to play with abandon in front of people than it is to produce a sound from inside yourself that you are happy for other people to hear.
I like to think I am the encouraging type of teacher. I never say anything is bad, unless it is an intermediate or advanced student I have worked with for a while and I know they want constructive criticism and that they can take it. With beginners and scaredy cats I find the softly, softly approach works far better than shooting them down the first opportunity I get. I find that even the most confident people in life can be riddled with fear if asked to sing on their own. This fear can also apply to group singing. The fear that you will come in at the wrong time or keep singing when everyone else has stopped singing can be, for some, a risk not worth taking causing the student to sing in nothing more than a whisper. Case in point:
One group I teach is made up of 10 highly exuberant teenagers. All have something to say, many of them are hilarious and they are all very chatty (sometimes to the point that I want to tear my hair out). However, the minute I ask them to sing the volume goes down to the level you would hear in a library. This annoys me for many reasons, the main one being, I know for a fact, that they can all sing in tune and all have pleasant voices (some have great voices) but ask them to sing together and the fear takes over. I have made headway with some of them and they have started singing out a little more and I am hoping this will encourage the rest of the class. The main culprit for lack of noise, though, is the fact that they will not open their mouths.
I have to stop myself telling these and other children to stop being silly and just sing for goodness sake as I know it will have the opposite effect. It has to be coaxed out of them, but my advice to all beginner singers is just open your mouth and let the sound out. I promise you won't regret it.