Today, it's often taken for granted or as a truism that heroes don't kill (despite plenty of evidence historically and in fiction to the contrary). In fact, it is often taken to the extreme that the heroic ideal ought never kill under any circumstance, situation, exception, or excuse - or otherwise deny their right to be a hero. The in-story rationales are often paper-thin, unrealistic tautologies: "because we don't."
Several trace this to the mid-1950s, Fredric Wertham's attacks and congressional hearings and the subsequent Comics Code Authority, but Batman and Superman had already been reined in by Frederick Whitney Ellsworth, editorial director of DC, over a decade earlier. According to Slate, responding to parental censure and an editorial in the Chicago Daily News, Ellsworth told Batman writer Bill Finger that Batman should "never carry a gun again."
What is the earliest example of a heroic figure with an absolute prohibition on killing?
I am not speaking about situational mercy (like David refusing to cut down Saul) or a general view that unnecessary killing is bad and to be avoided. Instead, the more extreme position that there are no situations where killing is permissible, moral, excusable, acceptable, allowable, justified, or tolerated for a hero (because this position is always outwardly hypocritical in that others may justifiably kill sometimes but not the hero; ex: Batman allowing Alfred to arm himself with a shotgun or working with police armed with sidearms).
The Lone Ranger comes to mind who, despite his trademark silver bullets, is said to fire his gun only to disarm, believing only the justice system can mete out a final disposition for lawbreakers. Are there earlier examples of such absolutists?
I tend to believe these are outliers and exceptions to the rule, because it seems like the vast majority of pop culture endorses the occasional need for death. And perhaps not-so-occasional when it comes to the Marvel Cinematic Universe with an estimated body count of 5,002,617 (Infinity War excluded for reasons). Nonetheless, I still routinely hear the rationales raised even though it doesn't jibe with thousands of years of hero stories and even our present day heroic narratives.
Is the absolute prohibition pervasive and, if so, when did it become accepted?
When did "There's always another way." become a thing?
Not just an observation of what was happening but asserted as a value and truism in-story?