What does the savage realize he should do after watching Linda die?

John realizes that he has to take a stance in the midst of people with no feelings, morality or values. He immediately and loudly speaks against soma...... one of the things (poison) that has desensitized the people to emotions.

Linda had been a slave, Linda had died; others should live in freedom, and the world be made beautiful. A reparation, a duty. And suddenly it was luminously clear to the Savage what he must do; it was as though a shutter had been opened, a curtain drawn back.

"Now," said the Deputy Sub-Bursar.

Another khaki female stepped forward.

"Stop!" called the Savage in a loud and ringing voice. "Stop!"

He pushed his way to the table; the Deltas stared at him with astonishment.

"Ford!" said the Deputy Sub-Bursar, below his breath. "It's the Savage." He felt scared.

"Listen, I beg of you," cried the Savage earnestly. "Lend me your ears …" He had never spoken in public before, and found it very difficult to express what he wanted to say. "Don't take that horrible stuff. It's poison, it's poison."