By that logic, why did people throw a shitfit when Star Wars Episode 8 came out?
Why did people get so mad when Superman snapped the neck of one the last survivors or Krypton.
Why did people get mad when Batman had machine guns on his batmobile and had total disregard for human life
I can go on and on.
But in fiction a character gets solidified in the cultural zeitgeist and it becomes the character.
For Snyder to even imagine doing this shows either hubris or a total lack of understanding.
I think it was a lot of both.