The idea that Snape is struggling toward redemption is popular with readers who believe in his innocence. Like everything about Snape in the Potterverse, the evidence is ambiguous. It’s all a matter of how we interpret Snape’s actions. If we believe in Snape’s loyalty, we can intuit Snape’s desire for redemption from his turning spy for Dumbledore (‘“at great personal risk”’ [Goblet of Fire 591]), from his expression of remorse, from his protection of Harry, and from his work for the Order.
And, if we believe in Snape’s loyalty to Dumbledore, we should consider for a moment what this loyalty requires of Snape. He is asked to protect the son of the bully who emotionally scarred him; spy on a mass-murdering despot, kill the man who took him in and gave him a second chance, and be reviled as a betrayer. And, oh yeah, Voldemort is probably going to Crucio him into the next century for thwarting his plan to have Draco die attempting to kill Dumbledore. Only someone with a serious commitment to atonement would agree to a deal like that.
Joyce Millman, “In Defense of Snape” from “The Case for Snape’s Innocence” in The Great Snape Debate, 2007, p. 13,15
# In 2007, Borders (RIP/requiescat in pace) published a book called The Great Snape Debate, in which various authors laid out “The Case for Snape’s Innocence” and “The Case for Snape’s Guilt”. I remember reading it before J. K. Rowling’s Harry Potter and the Deathly Hallows was released.
# Remember those days in the fandom?