The final exchange between Pero and Atlas is sad in that the latter really feels that he must do what he does to survive, and really just how badly people like him are pushed to their breaking point because of Duke Red.
Atlas: *pauses for a moment* There's no simple answer to that question...yes I agree that we're a violent race controlled by emotions, they're at war within us, and we can do nothing but move forward in search of peace through destruction! If we deny their existence then we cannot survive, and without emotions *cocks his gun*...then we are nothing.
No matter how you feel about Atlas killing Pero... it is sad that everything he ever worked for was destroyed afterwards, thanks to Skunk. He may have been bigoted towards robots, but he genuinely cared about the people around him suffering from poverty and clearly had humanity in him as evidenced by his willingness to stop one of his members from killing Kenichi and Tima. Watching Atlas bleed to death, realizing he was set up can be heartbreaking for those who sympathized with him. That's more than you can say about Rock...
When the lowly garbage bot Fifi sacrifices itself to stall Rock long enough for Kenichi and Tima to get away. Just a moment before it wasn't willing to follow them in fear of going "out of bounds".
Turns into a happy Tear Jerker later when Fifi has fixed itself.
