Comics became “dark” in the 80’s for two main reasons. This first is and ageing market. Comics customers have become loyal buyers instead of fast loyal kids. Fandoms were empires of preferences and predilections that writers had to work in. the biggest goal for a comics writer would be to write a story so good fans of another hero would need to pick it up. On the lowest levels they needed to create continuity to their story without making it to clichéd for their character. It was a new generation of writers in a whole new selling situation and they found the creative freedom they needed by using back stories that were already there and creating the personalities that should have come from them. These writers took the hero’s down from their pedestals and made them walk among mortal humans, if not below them. Justice became hazy, like it really is, and therefore the heroes sold well enough.
The second reason comics became darker was because of the question of what justice was in the U.S. was becoming less clear. While segregation ended in 1964 most of the major Supreme Court cases in this decade deal with what is and is not appropriate in a desegregated work environment. Sexual harassment also became a thing so that probably made lots of men who didn’t realize objectifying women was bad, sad and since most comic readers where white and male (what are you gonna do?) they turned to comic books that depict #whiteboyproblems. Every oppressed group gained something in the 80’s but the white male was only brought “down” to be equal with all of them. In the world of the Super hero these white males had conflicts and post traumatic stress, but they were still manly men. Is it fair that now everyone is equal, probably, but in fiction the world can look any way you want it to.