Post-Crisis Superman was born in the United States. He was conceived on Krypton, but his gestation pod was fitted with a hyperdrive and sent to Kansas, so he is a jus soli US citizen.
I assume that's been retconned to make him Krypton-born again. But since his origins were unknown until he was an adult, that makes him a foundling, and he is a US citizen at birth under INA 301 (8 USC 1401).
Superman has (or at least had) a great supporting cast and a rich, well-developed world. That's why they could kill him off and keep going without missing a beat--all the other characters were so interesting, DC could (and did) tell stories about them for months before Superman came back.
He would never hurl a child-rapist (or even a child rapist) into the sun because he believes all life has value, coming as he does from a dead world. Not unlike Batman, who would never kill his broken, pitiful enemies because if there's no hope for them, there's no hope for him, either. And both operate outside the law but with its tacit approval, which requires some self-imposed limits.