Mr. White's view of the monkey's paw is not consistent. It changes over the story.
In the beginning of the story, he is intrigued by the paw. He probably does not believe in the tales of the paw wholeheartedly, but he believes in them enough to save the paw from the fire. When Sergeant Major Morris throws the paw into the fire, he snatches it out of the fire and saves it. This action shows, in the least, some interest in the paw.
When he actually makes a wish, 200 pounds to pay off the house, he values the paw enough to make a wish. However, his view changes shortly thereafter, because the money comes at the expense of the death of his son. He is confused. Did the wish do this? Was it coincidence?
When he asks for the life of son again, his view of the paw changes again. He fears it, but he believes in it enough to make another wish. When he hears a knock on the door, he frantically searches for the paw to make it all go away. At this point, we can only guess at this views of the paw. It is probably a mixture of fear, hatred, and confusion.