Killing you

"I will kill you!" He screamed fiercly, preparing to stab deeply the knife into the victim's throat.
"No, you won't," said Will, fearless and way too calm comparing to a man who has just heard such sentence.
"I want to kill you. I MUST kill you."
"Why?"
"Because they said so."
"WHO said so?"
"They."
"And…?"
"If I don't do that, I will die."
"So you prefer to be a murderer than being dead."
"I don't have many choices."
"But what if you kill them?"
"I can't."
"Why?"
"They're stronger."
"How stronger?"
"Too strong for me."
"And if you use this knife?"
"They have much more."
"But you have one thing they don't."
"Which is?"
"Nothing to lose…"