My theory is that the true villains are the castle staff. Look at Chip. He is about 4 or 5, meaning they don't age and their curse is permanent. The beast ages and will die however. My thought is that the castle staff was raising him for great evil. She was sent to destroy them all, but having a good heart decided to enchant the beast and all of the staff, hoping they could learn a lesson instead. At the worst the beast would die of old age unable to bring suffering on the people. It was a mercy not a curse.