Not all Dark heros killed, To me a dark hero is the mood of the comic, I almost temtped in putting Dick Tracy as a dark hero, because one he kills, and 2 the mood of the comic, 1930's the great depression, mobs, gangs, the era of Bonnie and Clyde, Babe Face Nelson, Pretty Boy flody, John Dillarder, and many more gangsters of the 30's. It was a very dark and moody era, and Dick Tracy caught it perfect.
So does Batman since in a way is 1930's dark mood.
Shadow as the 1920's jazz. But it too has the same dark mood of the villians, Shadow kills too.
How I ranked the DARK heros are
Shadow, I like the line "Who knows what evil lurks in the hearts of men only the shadow knows"
Batman, He is dark.
Punisher,
Crow,
Blade
Hunter D and other vampire like killers
a few other, but Shadow is tops imo.