than having the villain(s) slowly trying to laser blast people to death while superman held the villain in a position where he could easily move them but decides to kill them instead.
Do you really think Superman's only motive for killing Zod was to stop him from killing that family?
I don't think so. The killing of Zod needs to be seen in the context of all the destruction and death Zod had done up to that point.
The family was just the last straw. Zod's behavior made it clear (and he even told Superman that this was a fight to the death) that the only way he would be stopped in his plans for the destruction of earth and the reestablishing of Krypton was to kill him.