First, even though he was a Death Eater, he was on Dumbledore's side. He risked his life getting information for Dumbledore from Voldemort's side. The professor killed Dumbledore only because he asked him to. Snape protected Harry once Dumbledore was dead even though he hated him. He worked for Dumbledore through all of Harry's years at Hogwarts, and before.
Second, Snape saw Harry as Harry's parents in one. When Harry was walking down the halls at Hogwarts, Snape would see the back of his head and imagine it was James, the person he hated. When Harry would turn around, his eyes would meet Harry's and Snape would see Lily, the one he loved. He would have to deal with the fact that Lily was dead and that she had loved the person he hated most. Snape's life only got harder because he saw Harry as Lily and James in one.
Lastly, without Snape's help, Harry would have never destroyed Voldemort. Snape provided Harry with the sword that helped Harry destroy the locket that had caused the three friends much pain. When he died, he gave Harry his memories that told Harry he must die, or Voldemort would never be destroyed. In the sixth book, Snape's potion book told Harry about the Bezoar Stone that saved Ron when he almost died. Snape helped Harry and his friends a lot. Without him, the story would not end happily.
In conclusion, Snape is a hero. He was on Dumbledore's side. It would be hard to be nice to someone who he loved, hated, and was angry at, at the same time. Lastly, he was helping Harry. Snape was truely a good person to so many, and he was one of the most important characters. So lets all hail Snape, because he is a hero!
