I think there is a very well-founded fear of cuts in the cords and casing, as that can have unpredictable and very unpleasant results. But we seem to agree that simple tread cuts aren't in of themselves grounds for discarding a tire. The key issue is having the good judgment to assess which category it falls into and act accordingly. As someone else noted, an inspection of the tire from the inside can help assess if there is cord or casing damage.