I was Re-watching Harry Potter and the Philosopher’s Stone and I realized that the Dursleys not only failed Harry (which they did majorly), they failed Dudley as well.
By spoiling him and enabling him to bully and belittle others from such a young age they are partly what made him the way he was.
Like how they showed him to be greedy by showering him with presents on his birthday and not objecting or telling him he should be grateful when he complained and asked for more.
Or by turning the other way (and even encouraging him) when he bullied other children, especially Harry.
It was their responsibility to teach him right from wrong and they failed.
I am not saying Dudley is completely innocent or that he is stuck being a greedy bully but they certainly didn’t do him any favours.“Dumbledore paused, and although his voice remained light and calm, and he gave no obvious sign of anger, Harry felt a kind of chill emanating from him and noticed that the Dursleys drew very slightly closer together.
'You did not do as I asked. You have never treated Harry as a son. He has known nothing but neglect and often cruelty at your hands. The best that can be said is that he has at least escaped the appalling damage you have inflicted upon the unfortunate boy sitting between you.'”
― J.K. Rowling, Harry Potter and the Half-Blood Prince