They're good books (humanity are THE most warlike species in the universe and it's their only advantage), but I don't think that's the source of the quote. It sounds like something from Subspace Encounter, by EE 'Doc' Smith (the same guy who gave us the Lensmen). As the book was completed after Doc's death by Lloyd Arthur Esbach, I don't know which of them actually wrote the passage I'm thinking of:
"...the deadliest possible performer is not the one whose ordinary life is violence, but a highly intelligent entity who, having coldly and accurately evaluated a situation and having come to a decision, proceeds coldly and ruthlessly to take whatever action is necessary to implement that decision."
D for Drakensis
You're only young once, but immaturity is forever.
"...the deadliest possible performer is not the one whose ordinary life is violence, but a highly intelligent entity who, having coldly and accurately evaluated a situation and having come to a decision, proceeds coldly and ruthlessly to take whatever action is necessary to implement that decision."
D for Drakensis
You're only young once, but immaturity is forever.