Of the three, Wonder Woman was the most visibly shaken by Superman's choice to kill Lex Luthor.
Diana's origins in an isolated society of immortals, perhaps was the cause. With a new costume, it is inferred that Diana renounced her Amazonian heritage, since such a lifestyle directly conflicted with the Justice Lords' new brand of justice.
However, she still shares some level of compassion for humans. When the Lords confronted Doomsday, Diana saved a train from falling off the rail. Despite that she is still willing to kill, even the League's Batman.