I don't agree with getting rid of the heads-up alert that there are new players for a dungeon. I think it is helpful and useful to see. One can set their expectations with the knowledge that at least one person is new.

If you are encountering people who are quitting just because of that message then count your blessings that you didn't have to run the instance with them. Clearly, they need to be carried through the instance and don't know how to do it without others carrying them. (That is written with only a little tongue in cheek.)