1) Who said that if he has wooden stairs that they would be polished?Irrelevant , common sense , polished step is slippery , slippery stairs is dangerous.
2) The world is full of dangers - common sense demands that you rank them in importance.
Common sense says that if you want to use a figure of "4000 falls by children on stairs" to prove that people should not have stairs which are not carpeted then you must know over what period those 4000 falls occurred (e.g. an average of 40 per year over a 100 year period is not the same as 4000 per year), and you must know if they were all proven to be due to lack of carpets, and you must be able to put them in perspective by comparing them with the number of falls occasioned by ill fitting or damaged carpets.
Otherwise you haven't got common sense, you've got superstition, old wives tales, etc.