It's all but stated that Thrackerzod is a demon inhabiting the body of the real Sweetie Belle. So, what ever happened to the real Sweetie Belle's personality? Either she is trapped within her own body somewhere in a pure state of And I Must Scream, or her original being has been completely destroyed.
Rarity also says that Sweetie Belle has called herself Thrackerzod 'as long as (she) could remember' implying that perhaps there is no original Sweetie Belle, and Rarity's mother was somehow impregnated with a space parasite.
Although, since we haven't seen what Thrackerzod was like before possessing Sweetie, it's still possible their personalities were fused together... Which may be even more creepy, but at least she'd still be alive.
I mean let's be honest, no one noticing her possession because Sweetie has the same exact personality would be in line with this canon. Now I wish we could see Sweetie and Thrackerzod as headmates/roomies.
The thought of how Twilight's life has been completely ruined by Celestia's "teachings". Who knows how better off Twilight would be if she'd never been accepted as Celestia's "faithful student". Also, since Celestia is thousands of years old, how many others could she have done this to?
Though Pinkie Pie may be an Ass Hole Victim, the way the Equestrian Health Care system completely abandoned her in RDP: Bitter Sweet had absolutely nothing to do with anything she had done. Is that how Equestria's health care system treats everyone that can't afford medicine?
Why does Spike still worry about Twilight and act as if she's his friend in episode 22, when he constantly complains about her treating him as a slave and she treats him like crap? Because she's just as much a slave, as he is. With how Celestia's relationship with her is shown, she's probably not in a particularly better situation. They're both in a place in life where they have no real control over what happens to them, so if nothing else, they can at least try to be friendly with each other after all is said and done.
Why is Twilight almost completely apathetic to Fluttershy? Because she has it a million times worse with Celestia, so instead of feeling sorry for some "yellow girl" who can't even stand up for herself and make her say her actual name, she brushes her off, because everyone has their own problems to deal with.
If a male-female voices are the inverted in the Mentally Advanced Universe, then it only makes sense for Spike to be voiced by a guy too.
