That moment Brian realizes he hear voices

The scene in the studio? That is a great scene.

I'm not sure if it is meant to convey the first time he was hearing voices. Brian says that he certainly always heard his father's voice telling him to buck-up and this and that. By the time of Pet Sounds his growing sensitivity and facility with music may well have combined with his feelings of anxiety so that the sounds he heard in his head, good and bad, were competing with each other. And just as he was having great success with the music, the bad stuff was gaining equal prominence.

The scene definitely acknowledges his hopelessnes. If the guys wont trust him with the music then how are they going to deal with this? Tragically, it meant that Brian accepted it and prayed that his own willpower and forging ahead with the music would straighten everything out. He constantly talked about the healing power of music and laughter around that time, but and when that failed he moved on to stronger "medicine" and the rest is history.

Glasgow's FOREMOST authority Italics = irony. Infer the opposite please.