chp 51-54 & A/N

Is it plausible that Harry would go along with this rescue? It is harder to accept than a Sirius rescue, which would've been based on the belief that Sirius was actually innocent (he hadn't done the awful things he was convicted of). The extenuating circumstance of having become evil under the influence of the Dark Lord provides a much weaker reason to rescue someone, and requires much more trust in the person who is conveying the information (since they must not only get the facts right, but make some subtle and complex judgments about the prisoner's character and what they deserve).

If Quirrell had just come straight out and asked Harry to help him break Bellatrix Black out of Azkaban, and to pretend to be Voldemort while doing it so that she would follow him out, I don't think he would have done it. Far too many red flags. Sure, Harry wants to end Azkaban, but to start with Bellatrix, who undeniably did so many evil things? Quirrell's case in favor of Bellatrix's innocence sounds like what a partisan would say when trying to make their side seem favorable, not an argument that Harry would buy (just as he could see through Draco's case against Dumbledore). Genre savvy Harry has read plenty of stories about villains with a sympathetic backstory.

Harry knows that Dumbledore doesn't trust Quirrell, he can imagine how Hermione would react to this (and she was right about transfiguration experimentation), or how Neville would react (Neville, who said with his voice shaking that torturing his parents was "not even close to the worst thing she's ever done").

Or even how Draco would react: Bellatrix Black? She was one of the few who were truly evil (chp 47). Forget that nonsense about wanting to save a poor innocent person from the nasty Dementors (you really think that's why Quirrell wants to break someone out of Azkaban?), this is obviously part of a plot. As Father would ask, who benefits? What kind of plot would involve breaking Bellatrix Black out of Azkaban?

But Quirrell didn't just come right out and suggest that they go free Bellatrix from Azkaban, he gradually and artfully got Harry to buy into the plot. So if we're going to wonder whether it's plausible for Harry to go along with it, we'll have to look at how Quirrell manipulated him into agreeing, and why Harry fell for the manipulations and wasn't stopped by these red flags.