Dewclaws are barely attached to the foot, and certainly not with joint, cartilage and bone. When you declaw your cat, you cut off its fingertips, sever the nerves, and prevent the cat from accomplishing normal and required psychological behaviours (grooming, scratching, etc). There can never be any moral justification for that - "oh, it was a kitten and it was scratching my furniture!" Yeah well, that's what kittens DO. It's called training.