But then it turns out that his arc over the course of Dawn Of Justice is learning that Superman isn't so bad. Not from getting a new perspective on the event, like learning that Superman had no choice or that Zod killed most of the innocent people (neither of those things is true), but from getting to know Superman as a bro. First, he learns that Superman is fighting for his mother, Martha, and then he sees Doomsday. By the end, after Superman sacrifices himself to kill Doomsday (told you there'd be spoilers), Batman says: "Men are still good. We fight, we kill, we betray one another, but we can rebuild. We can do better. We will. We have to."
Putting aside the fact that this makes precisely zero sense (why does Superman, an alien, sacrificing himself to stop Doomsday, an alien created by an evil human, give Batman faith in people?), the point is we watch Batman learn that Superman was right all along, and we shouldn't hold him accountable for the deaths in the movie. Superman is beyond any concept of being held responsible for his actions, because ... uh, his mother's name is Martha, I guess.
Just wait until Clark Kent finds out what happens in Hollywoodland.