"Batman does not spare Superman because their mothers share the same name. Batman has spent 18 months obsessing over killing this alien who can destroy the Earth. It isn't until Superman uses the name that the alien becomes humanized. At first, Batman becomes even MORE enraged because he thinks it's another trick. Once he realizes it's Clark's mom's name he starts to understand that maybe they're not so different. He never considered the evil alien had a human mother or let alone would be willing to die for her. Bruce couldn't save his mother. No matter how many goons Batman brands, he was a helpless kid when she was killed just like Clark is now. He'll never be able to bring his Martha back. Now he has an opportunity for redemption. It literally has nothing to do with their mothers having the same name, that was just the spark(that you can see snapping Bruce out of his kill rage) that showed him Superman wasn't pure evil. With potentially his last breath he asked his killer to save someone else. There's no argument. It's not confusing. It's not grasping at straws. It's in the narrative. It's the entire reason we were shown the murders of the Waynes one more time. This moment goes down as one of the biggest problems amongst the dissenters, when it's actually one of the most emotionally stirring and theme appropriate scenes if you're paying attention."
lol people understood the reasoning fine. People just think it's cheesy and ham-fisted. For one it requires Superman saying "Save Martha" instead of "Save my Mom" like a normal person. Then Lois needs to interrupt the scene to explain it. Everything about it is delivered in the most cheesy and hilarious way.
You can't just judge the scene based on intentions. It's not exactly hard to build up to Batman empathizing with Superman through his own personal tragedy and that resolving the conflict. But the execution was poor. Just like any other attempts at being emotionally stirring from the movie.