This would have been a perfect vehicle for an anime series.
Ender’s killing of the bully is horrifying, because it’s so cold blooded. Merely a weighing of options, benefits, and outcomes. No thought about the moral implications.
A theme, btw, that runs throughout the entire book.
He didn't intend to kill the kid. He wanted to send a message that he wasn't to be messed with by bullies. I actually was pretty impressed by that scene.