The idea is when so much of our agency is stripped from us, often the last thing we can hold onto—which we hold onto tightly because it is the last thing—is comtempt. You can crush me under your boot. You can make me sing the party's songs. But you can't make me believe them. You may own my body but not my mind.
We in the US are living in a time of deep cynicism and distrust of all of the institutions Americans used to hold dear. The degree to which that distrust is misplaced is an open question but the distrust itself is unequivocal.
I look at the current culture of anti-heroes and dark superheroes as a reaction to that. We are so distrustful of anyone or thing claiming to be good that a brightly-colored positive superhero today would earn only contempt from us. We'd assume it must be a deceitful facade.
All that leaves us is morally corrupted dark anti-heroes that are least openly flawed and whose contempt for the other institutions of justice mirrors our own.