I see where you are coming from, judging and positive criticism are two different things, but it all depends on how things are said.
Individuals who get heated up due to positive criticism, may either have a bit too much pride or may have forgotten how to be humble.
Sometimes our attitudes by no means reflect our playing... it's better to be someone who doesn't know how good they are then to be someone who acts as if/ thinks they are better than they are, and can't musically deliver.
we should pay attention to respected musicians around us, as it is better for them to say something then for someone else that you may not know to say something.
but some people just don't like anybody commenting (encouraging, or getting them to think another way) and may feel teh individual is trying to tell them what to do, just as God gives us the gift to play, he allows us to fall upon the right people tohelp us improve and aim to perfect the gifts and ministries he has given us.
this is how i look at it, you don't know where God's going to take you with the ministry and gifts he's given you, but while going through the process of preparation (i.e. playing at church) you should listen to others, it's better than going out (various events) and some complete stranger saying to you what your local folk wanted to but you wouldn't allow them to.