This is what made me think of the saying "the sins of the father" because that is ultimately what everyone is learning their ways from. It all begins with the elder Earnshaw and his irresponsible ways of parenting. He brings an orphan home and instead of making him part of his family, he sets him apart from the other children, playing favorites and making the relationship between all of the children very strained. He was the origin of the animosity, "Nay, Cathy, I cannot love thee; thou'rt worse than thy brother. Go say thy prayers,child, and ask God's pardon. I doubt thy mother and I must rue that we ever reared thee!" It cannot be a mystery as to the reason that there was outward hatred, especially between Heathcliff and Hindley.
Years later, that relationship only gets worse, and with the death of his wife, Hindley pretty much loses his mind. He becomes a violent alcoholic, bent on revenge. The household becomes tumultuous and no one seems to be learning anything from their situation. Instead, they all just sink deeper into their own sufferings and don't learn a thing from what they are going through.
With the next generation you see the same thing. Hareton becomes a fowl child, mimicking his father and Heathcliff instead of seeing how horrible their lives are and trying to distance himself. Its just a cycle from generation to generation. The younger ones always paying for the mistakes of their elders by thinking that that is the only way to live. Forgive and forget is not an option for these people.
I feel that this can sometimes still be seen in modern day society, where the mistakes of the parents negatively affect how the children grow and develop. This is ultimately, I feel, a main cause for the perversion of all of the characters of the story.
