>>715477802 (OP)
it went against Venom's nature as a medic who wanted to save and preserve life rather than take it, or facilitate conditions that would cause a loss of life (such as war)
when Venom talks about the "demon" inside of him, it's Big Boss's bloody inclinations and hunger for conflict that he's talking about, the personality that was implanted upon him. he had such an idealized vision of who Big Boss was and didn't realize how wrong it was until he became the man himself.