Harry Potter and the Order of the Phoenix Theme of Hate

We've seen a lot of bigotry in the Harry Potter series before. Draco Malfoy calls Hermione a Mudblood, meaning that she's a magic-user with non-magical parents. Then there's the Death Eater "prank" at the beginning of Book 4, when they levitate a Muggle family through the campground at the Quidditch World Cup because they enjoy torturing Muggles. But the hatred in Harry Potter and the Order of the Phoenix has a slightly different character.

Professor Umbridge hates half-humans, so she also has racial prejudice. But her hatred is largely aimed at people who disrespect her authority. Professor Umbridge loves rules. When she first comes in to the classroom, she insists that the students answer her with a full, "Yes, Professor Umbridge" or "No, Professor Umbridge." She wants them to show their obedience to her at all times. And when a student – ahem, Harry – doesn't immediately obey her, she turns the most terrifying loathing onto them. The thing is, Professor Umbridge's name is notably close to "umbrage," meaning to take offense. Everything offends Professor Umbridge, and she hates anything that offends her. So, by association, Professor Umbridge pretty much hates everything. And her hatred sours the whole atmosphere of Hogwarts throughout Book 5.

1. We see several different examples of magical creatures hating humans in Book 5. On what grounds do these creatures claim to hate humankind? Do the different magical species we see in the novel hate humans for the same reasons? Why does J.K. Rowling take care to represent this hatred in Book 5?
2. Sirius's hatred for his family leads him to treat Kreacher as something less than a person. What other examples are there in Book 5 of hatred leading normally good people to behave cruelly? How does their behavior change your view of their character? Is what they do excusable? Why or why not?
3. There's plenty of school rivalry at Hogwarts, particularly between Slytherin and Gryffindor. When does ordinary rivalry seem to turn into hatred? What leads Hogwarts students to hate each other? Why does the Sorting Hat decide to sing its warning against division now, in Book 5?