"They hit us, so we hit them back."

That's the nature of the business - the Family Business. Santino was not a psychopath - he never got his hands dirty, so far as I know. I read the novel, but don't get a notion that Santino actually committed murder by his own hand. Ordering hits is another thing. It's almost like a game.

Bruno Tattaglia murdered Luca. Bruno was no saint. Santino's mission was to protect the Family, and that's what he was doing. Calling him a psychopath is a little much. Do you view Vito the same way?