The Starchild

I wasn't uncomfortable with those things at all. Plenty of movies and even cartoons on TV have been just as dark before and MLP has been plenty dark itself. As a matter of fact, I really liked those elements. I didn't like what the film did to "We Got the Beat," but that was the only time I was uncomfortable.

Well, I'm unfamiliar with the "discussion about Starlight the villain or Starlight, Twilight's student," but she has returned to the village since the incident and they did indeed all forgive her. They were glad to see her come back and honestly, I think they'd welcome her with open hooves if she wanted to move back. She wasn't treated any differently and since she did repent, she shouldn't be.

Well, in Season 1 we both hear that Rainbow is the only one who ever pulled it off, and in a later episode, that it was a legendary thing prior to her existence. So the current lore is already a bit shaky. If we assume that it is indeed the stuff of legends, one that ponies already knew about before Rainbow Dash pulled off her first one as a filly, then there is absolutely no reason why another pegasus wouldn't be able to do it, too. However, ponies capable of the feat would theoretically be few and far between or it wouldn't exactly be anything special and there'd be no legends about it nor would it be a big deal. So, more than one pony being capable of it in the same era seems like a thing that wouldn't be highly likely to happen. I'm not saying it shouldn't happen, by any means. Just if it does, they can't start introducing more and more characters who can do it. One showing up (or reappearing) to challenge Rainbow could make for an interesting episode, or even a more drawn out rivalry. They'd just have to not get carried away with it.