How come the Avengers can kill people left and right and no one bats an eye but Superman cant kill an unstoppable alien killing machine (and cry about it too) without people freaking out?
Cause deep down, people FEAR Superman and fear what he can do if he gets pissed off. We seen in the "Injustice" games when Superman loses everything he loved and went on a spree, and saw how other heroes were and even going when he was relentlessly killing.
People in modern times hate Superman because he is "perfect" in order to justify their own shortcomings in life, but they FEAR on what he represents because they can never have his heart or his selflessness. So, they resort on clowning him instead.