"Muh Supaman neva kilz, muh Supaman always finds another way"
There is a HUGE difference between killing Zod because it was necesarry at the moment and Batman killing criminals because they stand in a way and he is too angry to care anymore, because 25 years in Gotham broke his faith in goodness. On Vero Zack Snyder said his favorite Batman shot was when he walks out from the light reformed after witnessing Superman's sacrifice for humanity, which is why he later says that "Men are still good", he believes in that again thanks to Superman.
For Batman BvS was a redempion arc. Zack Snyder did not intended for people to feel ok with him killing left and right. It was meant to feel wrong so that his redemption arc would make sense and Superman's influence on people who lost their way was shown directly.
Anyway, I find it weird people defending criminals against superheroes. Some of them are monsters without any redeemable qualities, but people are ok with them being imprisoned and resources being wasted on them like food, water, electricity, air. It would be ok to kill someone like The Joker. It is not ok only because he brings in money and DC has to keep him alive for that so they came up with this ridiculous "code of honor" for Batman.