These threads, imo, serve entirely no purpose. The people who create these type of threads usually have a bias against the character and will cherry pick examples instead of doing an in depth analysis. It does nothing but promote fighting instead of having a good discussion. I admit I am not the biggest fan of Rainbow but I am also not going to take a huge crap on her character simply because I don't like her. She has her ups and downs just like the rest of the Mane 6. Now, with that mini rant out of the way, I am going to list three awesome things Rainbow has done.
Saved Rarity and the Wonderbolts. Followed Spike, with Twilight and Rarity, so make sure he was ok in Dragon Quest. Took Scootaloo under her wing.