You know why these 'Snape is changed after actually seeing Harry's life' stories doesn't make sense? First, he knows Petunia, how she treated Lily, and no way she treated Lily's son better. Second, he was teaching him Occlumency and Harry's memories should give even the stubbornest people a clue that he is the opposite of 'pampered prince'.
Why don't we just accept that Snape is miserable SOB who enjoys torturing Harry because he hated James?
Author's response
Well, obviously I can’t answer for EVERY one of these stories out there, but with regard to my own—firstly, as I did state, the fic doesn’t take into account the DH backstory, so in this universe Snape never actually knew Petunia. Secondly, we know he’s a stubborn sod who holds onto preconceived notions and who could probably excuse away a certain amount of evidence to the contrary. As for how much he could have seen or not in Harry’s head … it’s AU. Allow a little creative licence. I’ve considered exploring the thought that Harry’s worst memories of the Dursleys are buried pretty deeply, and Snape hasn’t actually accessed anything really concrete—nothing big enough to sway his convictions, at any rate. There’s not really the room for that in this fic though.