Wow, this poor old man gets so much hate. I used to dislike him, but as I get older and read more books, I now realize how much I act like him. I'm just going to list the some of the reasons people hate him and put my own word about it.

1.) "He left Harry in an abusive home"

If he didn't, Harry would have died in book 1. The only reason he lived was that Quirrell couldn't touch him. Why? Because of his mom's love protection. Why did it stay with him? Because he lived with the last living person who shares the same blood as Lily. Who is that? Petunia Dursley nee Evans. So basically, Dumbledore kinda saved his life.

2.) "He let Sirius rot in Azkaban without giving him a trial"

*sigh* Dumbledore has this habit of manipulating people to get what he wants. Yeah, sounds evil. But Sirius would have been in his was if he didn't go to Azkaban. Sirius would try to adopt Harry. What would happen? Well, either Dumbledore persuades Petunia and Vernon to live with both Sirius and Harry or Sirius just takes Harry. Option A is really unlikely. Option B would ruin EVERYTHING.  Read back to point one if you want more explanation. Sure, twelve years and Azkaban sucked, but hey, it was for the greater good.

3.) "He is so manipulative"

It wasn't for himself that he manipulated Snape and Harry. It was for the good of the wizarding community. Also, Dumbledore actually cared when people died. He just didn't show it.

Dumbledore wasn't a bad guy. Some people need to get hurt or die in the process of saving hundreds of people. Honestly, if the Sorting Hat sorted based on the characteristics a person possessed, not the ones they valued, Dumbledore would have done better in Slytherin. He's ambitious, resourceful and quite manipulative. But hey, I guess he valued bravery at the age of 11.