Myself I noticed a repeating theme in the DCEU villains in regards to a question almost all the movies ask in their own way, 'is mankind worth saving?' and the villains represent the answer 'no'.



Zod: No because humankind is less evolved than other older, more powerful cosmic races that 'deserve' to exist more.



Luthor: No, because humankind will always be corrupted by power.



Ares: No, because humankind will always choose to give into their lust for violence.



Ares I think makes one of the clearer arguments in that because of him Diana realizes that although she can battle the evils of man she cannot defeat the power of choice. And as long as people are able to choose between good and evil, there will always be evil in the world.

Diana left the battlefield no doubt because she would have felt like Sisyphus, pushing that boulder up a hill only for it to roll back down again and repeating for all eternity. Diana chose to leave the people and stay away from them because she realized, at his will, that Ares was in a way more part of the world (War) than a monster she could stop. I think Ares might be one of the more interesting vilians because he (the God of the War) was kind of right about mankind. He left the people of earth, yet the war was still a part of people. And I think it's precisely what made Diana lose hope before Superman's sacrifice reminded her that good deeds are never paid back but that they are still worth doing.



The example of what I mean may be Professor James Moriarty's speech in Sherlock Holmes: A Game of Shadows:



"You see ... hidden inside the unconscious is an insatiable desire for conflict. So you're not fighting me ... so much as you are the human condition. All I want to do is own the bullets and the bandages. War, On an industrial scale, is inevitable. They will do it themselves, within a few years. All i have to do ... is wait. Let's not waste anymore of each other's time ... we both know how this ends. "

What do you think?