Honestly, it seems pretty out of character for Sunny to react this way. I would think she knows a lot more about the importance of kindness. Especially since it was due to her kindness towards other ponies that she got her Alicorn abilities in the first place. And, throughout both Make your Mark and Tell your Tale, she has generally been the heart of the new group known as the Mane Five (or Mane Six, when Misty joined).

Next time. Get Fluttershy. Or Discord.