[nuconvert]

I don’t understand why Batman would fight Superman if they’re both on the side of Good?

[Rastus]

From what I understand, the fight between Supes and Zod in the first movie leveled a Wayne Industries building, killing hundreds of Wayne’s employees, so he sees Superman as a loose cannon who has to be taken down. In the movie, Batman’s been operating for years, and Superman was a complete unknown until that battle, so he doesn’t know or care about us motivation.

[Extremely Extreme Extremist]

This is why Batman and Superman are fighting:

Batman fights crime his way. Suddenly, Superman is swooping in to "save the day." But Batman (and the citizens of Gotham) are misinterpreting the way Superman fights for justice.

Batman sees Superman as a legitimate, if not unprecedented, threat to his city. So he's going to man up and take on this "supervillian."

What Batman does not know, is that Superman is a pawn for Lex Luthor for his own nefarious purposes. Once the two of them realizes this, they join forces, along with other superheroes in the background like Wonder Woman and Aquaman.

There. I just saved you $20 bucks in tickets and another $30 in popcorn in soda.

[SMGFan]

Bruce Wayne’s First introduction to Superman- an alien from another planet , and in the last film there was much destruction and death in Metropolis. Something personal to Wayne was destroyed .
There has been a history in comics of Batman having a documented plan on how to defeat any member of the JL if there were to go bad. Even if mind controlled by a villain. ie https://en.wikipedia.org/wiki/JLA:_Tower_of_Babel

[SMGFan]

Batman explains how to defeat the Justice League, including himself!

https://www.youtube.com/watch?v=ZJVvrmLSTsg

[Vince Ferrer]

In the comic book Dark Knight Returns , superheroes have been made illegal by treaty, with Superman the enforcer of the treaty. Superman is allowed to continue, but is really just a government weapon. Bruce Wayne is older, retired, but Gotham is falling into such a state that he can't stand it anymore and goes back to crime fighting. This sets up the eventual conflict between the two when the president eventually orders Superman to take down Batman. However, Bruce Wayne, with a decade to prepare for such a fight, wins.

[hattend]

I don’t understand how Batman can survive a single punch to orbit from Superman.