But see, Batman's killing (excuse me, refusal to save) is illogical because Ra could've been saved and then taken into custody by Gotham PD/the authorities who don't take kindly to attempts to kill/poison a city full of people. Batman also has a bit more a firmly established "code" against killing and Batman HAD a choice, Superman really didn't.
If Superman didn't act Zod would have killed the people and continued his rampage. If Batman acted Ra would've be imprisoned. Batman also came across as rather indifferent to the idea of killing (excuse me
"not saving") Ra.