Why did the Dursleys oppose Harry Potter entering Hogwarts?

Answer 1

There are a couple of reasons why the Dursleys oppose Harry's involvement in the Wizarding world:

1. The Durselys are obsessed with being "normal", and they consider all things magic-related to be "abnormal".

2. As a child, Petunia Dursley was extremely jealous of her sister Lily's powers.

3. It is hinted in later books that after the Potters were killed, the Dursleys distanced themselves from the Wizarding world as much as possible, because they were afraid that Voldemort might come after them next.

Answer 2

Petunia Dursley grew up extremely close to her sister Lily, that is until Lily met Severus Snape and found out that she was a witch. Petunia became jealous of her sister, especially when Lily went away to boarding school. In Petunia's eyes, Lily was the golden child who had betrayed her. Petunia even wrote to Hogwarts asking to be accepted.

She grew extremely jealous of her sister and the only way to cope was for her to hate magic. Petunia, along with her husband, spent most of their lives hating magic and getting as far away from it as possible. They were determined to stamp the magic out of Harry, unaware that this wasn't possible.