I'm less certain that part of the script proves the "exact opposite". Here's the next part of the script following that quote.
(The military has started firing K gas at Nor and Clark. Lois is urging Clark to get out of there.

form the script:
Quote
I can't leave him here.
(going to Nor)
He's still alive.

And he picks Nor up, fireman style, and begins to carry him
to safety.
So at the end, Clark could not kill Nor.

But, as I said above, I do agree that he could kill to protect someone else.

c.