I don't think gray morality in itself is horrible, it just needs its place.
Something like that though, there is no justice, its all black. Fighting for survival is fine, but in this case they're being forced to kill each other for the sake of it. The characters exist in a gray morality, but the concept is simply black.
With powers though, the idea of combat should be a last effort thing, which is why it works with black and white so well. If your motives don't overlap but your goal is the same, you work together and talk it out afterwards.
That's kinda the reason I don't like "dark" magical girls, they pretend a grey morality exist, but then shoehorn a bunch of black everywhere and pretend that it makes things grey.
In mahoiku for example we had>swimswim, retard kid who kills people when they're powerless without mercy or emotion (black)>ruler, complete bitch who mistreats her followers and tries to kill the nicest girl at the start (black)>angels, sociopaths (black)>tama, just a retard who didn't know what was going on (semi-grey, but mostly a non-character)>winterprison, lusting lesbian (selfish reasons, no morality involved)>nun, lusting lesbian who had a fetish for dying in her lover's arms (selfish reasons, no morality involved)>calamity mary, psychopathic murderer who beat her kid and joined the yakuza (black)>ripple, 'i almost got raped by my step dad so now I hate everything' turns into revenge whore (empathetic black)>boy, faggot who wanted to show off (non-character, selfish reasons just using powers to show off)>snow, innocent girl who runs away constantly and cries a lot, just wanted to help (later becomes a sociopath) (white)>top speed, only does things to protect people and flies away (white)>elf, evil murder hobo for murder hobo sake (black)>nemu, dies in her sleep, wouldn't of fought anyways (white)
There's no grey, its black and white hiding behind *BUT THEY WERE FORCED....!*