In the Monkey's Paw why does Major Morris throw the monkey's paw into the fire and why do the Whites react so strongly?

Major Morris throws the monkey's paw into the fire to try to keep anyone else from suffering because of it. He had kept it after using it, but now wants to destroy it, so that no one else would tempt fate by using powers beyond their control. White grabs it from the fire, and later uses it, to his lasting sorrow.

(see the story at the related link)