There is a great deal of difference between criticism per se and constructive criticism. In a teaching workshop I would be disappointed if the leader did not point out where I could do better - that is the whole point of going.

In general, if these people have been listening to others singing ballads in the past they will have got an idea of what is good and bad, what they are looking for now is an idea of what to do to be able to sing their chosen songs to the best advantage.

I can tell you, from personal experience, that I was unaware of a particular problem I had until Lisa Null was kind enough to give me some first class constructive criticism, which helped me improve my voice a lot. I did not find any problem in taking on board the advice of a first class teacher in a public group - those who do maybe shouldn't be looking for this sort of workshop.