I started hating Dumbledore during the third book... It became increasingly obvious to me that he wasn't as "light" and "good" as he seemed. My reason's include
1. Why did he not give Harry to Sirius?
2. He knew what life was like for Riddle in the orphanage yet continually allowed him to be sent back.
3. He knew that Harry was not treated well by the Dursley's, yet continually sent him back as well.
4. Forced Harry into a hero complex as to stop Voldemort.
5. Allowed Quirrel, Lockhart, and Umbridge to teach at the school.
6. Allowed students to be subjected to both a cerebus and dementors.
7. Made Harry watch his (Dumbledore's) death
8. Left out so much information about Harry that could have caused Harry to die in the war.