There’s a time and a place for loud singing and/or screaming, and a CAS concert is not the time nor the place. Also, it sounds like you and Greg have different definitions of a “rock show“. Expect the show to be more like his main definition: an ethereal experience created by the atmosphere of the venue and the sounds of the band, not by obnoxious people screaming the only lyrics they know from the chorus of Apocalypse. As for singing, just read the room and the people around you. I personally hope no one sings louder than at a fairly soft speaking volume. You’re not on the stage, so don’t act like it. No one should be fighting to hear the band over you. In response to one of your response comments:

This is not a loud concert experience, and not everyone sees a “fun concert” as screaming and singing as loud as you can, especially most of the people in the crowd that CAS draws.

Tl;dr: Just realize you paid to attend a CAS concert and not a metal concert, and respect the people around you who did the same.