Why does Sergeant Major Morris throw the monkey's paw onto the fire and why do the Whites react so strongly?

Often typical of horror stories, W.W. Jacobs short story "The Monkey's Paw" is about a group of seemingly good people who are drawn into evil by temptation. In this case, the Whites are a happy family whose lives are destroyed by their greed. When Sergeant Major Morris visits the family on a dark and stormy night he relates stories of his adventures in India and Mr. White cannot resist asking about a "monkey's paw" which Morris had mentioned in an earlier conversation. The paw is a magic talisman which apparently is able to grant three wishes to its current owner. When asked if he had made three wishes, Morris answers positively but never details what he wished for. It is only noted that his "blotchy face whitened" as he thought about it. He does, however, tell the Whites about the previous owner whose last wish was for death, adding that he had thought of selling the paw but that most people thought his story a "fairy tale." Then he throws the paw onto the fire, presumably a signal that the thing is evil and should be destroyed. It's also possible that this is simply a bit of dramatics from Morris in hopes that he may intrigue the Whites into buying it. Mr. White immediately retrieves it from the fire and, despite more warnings from Morris, decides to keep it. He ends up giving Morris a "trifle," probably a small amount of money for the paw. The Whites have obviously been lured into temptation by hearing Morris's stories and Mr. White eventually wishes for two hundred pounds which, unfortunately, proves a tragic mistake.