What turned Snape (Was: JKR site update SPOILERS)

[hickengruendler]

No: HPFGUIDX 158923

 
> Pippin:
> Um, but Dumbledore did tell Harry, though Harry was not listening
> very carefully. Dumbledore  was plain about it: "You have no idea 
of 
> the remorse Professor Snape felt when he realized how Lord 
> Voldemort interpreted the prophecy, Harry. I believe it to be the 
> greatest regret of his life and the reason that he returned--" 
> 
 
Hickengruendler:

Yes, but Dumbledore did not say, why Snape turned because Voldemort 
was targetting the Potters. Going after the Potters didn't make 
Voldemort morally worse, as if he would target random wizarding 
family X (say, the Longbottoms). And yet according to Dumbledore it 
was exactly this, that made Snape turn. Therefore it must have been a 
personal reason, which is related to the Potters. And I think if it 
were the Life Debt, than we and Harry would have been told this, 
because why make it a secret, if this motive of Snape is known since 
book 1. But we aren't told, therefore I believe it is not related to 
the debt or to James. It can't be because of Harry, because Snape 
surely didn't make any close personal connection to a baby. This 
leaves Lily.