You absolutely CAN tell that story, and they HAVE told that story.
If they have told that story, then why do I keep hearing about how the "no kill" code for Batman is sacrosanct and such an integral element of his character that to create a story in which it is violated is apocryphal and essentially DOA?
As for the difference between the wanton destruction and collateral damage, and preemptively killing Superman, yeah, that's true, and just further points out the pointlessness of the collateral killing in the first place. It is entirely superfluous if they're already taking him down the path of considering premeditated murder of Superman.
No, it is not superfluous at all. The collateral killing is the first line Batman's crosses (i.e. the line that leads him to
believe that he has gone past the point of no return, the point that he
believes he will totally lose control, etc.). The act of premeditated murder, however, is the line at which Batman has the potential to prove his own thesis -- move past mere belief to actual proof. Premeditated murder proves that one kind of killing unleashed a beast inside Bruce that cannot be tamed or controlled.
It also completely takes focus off that central dramatic struggle, as is undeniably apparent by the non stop harping discussion of it.
The central dramatic struggle is about whether heroes can be heroes if they are not all good or all powerful. Can heroism and goodness survive in a world determined to break heroes and demolish hope? The central dramatic struggle for Bruce is whether or not goodness and heroism is a beautiful lie. If there's any potential for evil (a one percent chance) that goodness is a lie, then should those who attempt to create goodness via the exercise of power be stopped before they inevitably fall?
Batman is convinced that Superman must die because he believes any flaw is grounds for believing that heroes are not all good and therefore can be corrupted. He embraces this idea because he's already down in that dark hole. It's why his worst nightmare turns Superman into a brutal killer who becomes brutal as a result of personal tragedy. Bruce identifies strongly with this. Like you said, he is convinced that once the code is violated, there is no turning back. Self-control of any kind is impossible.
If the story were just about Batman getting close to crossing his own point of no return and ultimately turning back, then there is no story about how Batman crossed that line and found a way back from descending into an absolute darkness beyond redemption. You can't tell a story about how Batman overcomes his fears of failure pushing him over an edge without actually allowing him to fail and tempting him with the edge.
In
Batman v Superman: Dawn of Justice, Batman crosses his self-created point of no return. He kills criminals or virtually ensures criminals will be killed. He self-identifies as a criminal. He is convinced no one good can stay that way. The only way forward he can see for himself is to pursue a suicide mission to hunt Superman to assure some sort of legacy. When Batman is able to stop himself from killing Superman, Batman saves Bruce. He saves himself from himself because he proves he can regain control after crossing the "no kill" code line. It isn't until Superman dies for humanity, however, that Batman genuinely believes "men are still good." Bruce now not only understands that he can control himself, but he can even believe goodness is still possible. Superman's death gives Batman hope.
