"You think you can threaten my mother?!"
(SWIPE LEFT). Superman obviously loves his mother, so imagine how helpless and powerless he felt when he knew if he tried to save his mother from Lex's grips she'd die. He couldn't do anything except "kill the Bat," because only then would she live. This is also the first time Lex has control over something more powerful than he. He could never recover from his father's abuse, so, he hates powerful figures. It's as simple. As. That.