For me, I would say cultural 100%, simply because I believe that no case of institutional discrimination is created without severe cultural discrimination. Thinks like slavery, segregation, police brutality, ect. all come from the common belief of and mistreatment of African Americans and those in the minority (whether minority by actual numbers or by lack of power). Although institutional discrimination is everywhere in TKM, these rules and ways of life come from the collective minds of those in power. Without individual discrimination, which then turns into cultural discrimination there would be no institutional discrimination.
Harper Lee likes to make a light of the institutional unfairness in the old south, but she makes it obvious that she knows the ideas of a community form and shape the rules they live by. The jury, despite seemingly being more or less leaning towards Atticus's side, chose the say guilty not because of fear of going to jail, but because the change of the status quo and the discrimination they then would go through are enough. They don't fear the rules, they fear what a "break" in the rules might cause.
After the trial ends and Tom is convicted, Atticus tells Jem ". . . The law says 'reasonable doubt', but I think a defendant's entitled to the shadow of a doubt. There's always the possibility, no matter how improbable, that he's innocent." (Lee 251) Although this seems like it would counteract my point by Atticus suggesting the law almost always goes one way, it's really about the jury. The law doesn't dictate that all African Americans accused of a crime are guilty, but at the time, the general opinion of the public does. That's why there's even room for doubt, or the shadow of a doubt, because institutionalized discrimination doesn't ask questions, it follows the rules, but cultural doesn't follow strict guidelines. This is why there is always the shadow of a doubt.
