@Starswirl  
I think that the themes pertaining to cutie marks seem to be childish at this point, which is why the discussion of them sounded so… not-in-character for her. I’m convinced that revelation could’ve been written MUCH better than it ended up being. Heck, we never learned how she got HER cutie mark…

@ShimmeringStallion  
Interesting. To me, Starlight actually came across as older than Twilight and her friends—until whenever she started talking about the Cutie Marks and special talents of others, at which point she sounded like a whiny twelve-year-old.

@Starswirl  
I never really saw it as “immaturity” as much as being Discord done right: He remains ignorant of Friendship in his early appearances, but it’s like she KNOWS she’s in a show about it, and doesn’t want to have anything to do with it.
 
It’s… brilliant, in a way… until, you know, things work out. :/

@ShimmeringStallion  
Heh, yes, that would’ve been funny! And it goes to show how immature Starlight really is.

@Starswirl  
Personally, I liked how in her original appearance at the start of the season, she would outright interrupt Twilight’s monologues and yell at her. I kind’ve hoped that would’ve been a running joke or something.
 
“You can do anythin~~”  
“SHUT UP!”  
“… Anything, as long~~”  
“Dooon’t…”  
“… as you~~”  
“DOOOOON’T…”  
“… hav~~”  
“DOOOOON’T!”  
“… Frieeeeeeee~”  
Starlight grinds her teeth in anger  
“~eeendship.”

@TB Tabby  
I understand your feelings. Honestly, her story didn’t seem that convincing to me either.
 
However, after thinking about it, I came to the conclusion that this is what Starlight blames for her deep-seated problems. Whenever she was enraged and not hiding behind her smug mask, she sounded like she was desperately jealous of other ponies. Of how they could find their places, be important, and form friendships despite their differences, when she herself was stuck in her self-imposed isolation. I believe it’s this self-loathing she projected on others, leading her to tear them down whenever she could.
 
And that’s why her losing Our Town was so tragic to Starlight. She went up against a group of friends she couldn’t break, who freed the ponies whom Starlight never gave a chance to be her friend to throw all her delusions and lies back in her face. It’s hard to recognise how ugly you are inside when you’re like Starlight; being angry at others is so much easier.

I missed this episode and got caught up via the TVTropes recap, and maybe I missed something, but THIS was her motivation for wanting to get rid of cutie marks?! She lost ONE friend because he got his cutie marks, therefore she assumed that EVERY friend she ever got would leave her because of getting their cutie marks?! Did she never observe OTHER ponies getting their cutie marks and not having to leave their friends? Did she not realize that her problem was actually a very rare occurrence?! And even if that WAS a likely scenario, she could avoid it simply by befriending ponies who already had their cutie marks! It should not have taken time travel shenanigans to show her that her objection to cutie marks was absurd! And this was the best backstory the writers could come up with?! Why not have her have been bullied for being a blank flank in a way that even Diamond Tiara would have objected to? Why not have her wanting to be the most talented pony in Equestria, but when she couldn’t rise above the others, she decided to drag them down?
 
But like I said, I missed the episode and had to catch up via TVTropes. Perhaps there are details the recap missed which make this backstory make sense.

@Background Pony Number 17  
Maybe they’re saving her reunion with Sunburst for the future?

I still think the writers missed a great opportunity during Starlight Glimmer’s redemption montage. We really should’ve been given a scene where at the end Twilight re-introduces her to a (now grown) Sunburst.

I’m sure she’ll wear it on her horn, always.
 
… or at least until gravity kicks in.