M'rk, son of Mogh wrote:
In that scene Superman practically begged Zod to relent, but Zod insisted. You could see the anguish in Superman's face as he knew what had to be done, but at the same time didn't want to do it. It went against everything he had been taught, everything he believed. In the end he saw no choice but to save that family that was about to be annihilated.
That's not murder.
I thought Superman was taught that life wasn't important, though? Isn't that what the scene with his father dying in the tornado is about? That a secret is much more valuable than human life, since life is only temporary anyways? But secrets and protecting yourself above all else, that's forever?
He basically murdered his father through inaction anyways.
The line was "I don't know. Maybe."
"Murder" implies intent. Clark wanted to run and save Jonathan, but his father said no. That's not murder.
In my opinion, Clark struggled with that and it clinched it for him. I think that if he were able to go back and change that one thing in his life, he would have saved Jonathan and dealt with the consequences later.
Call it a formative moment.