Tank. I won't argue with your idea of Superman's guilt, but as to whether or not killing Church would be more effective than taking him to prison, I believe Superman's actions were the most effective. Taking someone to jail can do some, but usually they can still post bail, or if not, they have lawyers who can get them off easy, plus they can still run their organization through communication with henchmen. By killing Church, Superman did send the message that their plans were over. Their leader is dead, and anybody who might take over is in jail. Therefore they would have immense trouble figuring out who would next lead the organization, if they tried at all.

I think, therefore, I get bananas.

When in doubt, think about time travel conundrums. You'll confuse yourself so you can forget what you were in doubt about.

What's the difference between ignorance, apathy, and ambivalence?
I don't know and I don't care one way or the other.