Both the Kerr and Schwarzschild metrics have coordinate singularities at certain values of the radial coordinate. Why is it that the "inside" of a Schwarzschild hole can be understood by using a coordinate transformation, whereas the "inside" (beyond the event horizon, not the ergosphere) of a Kerr hole is not so well understood? The only metric singularity in both cases is at zero radial coordinate, so there should be no problem. Are GR fags just lazy to deal with the complicated metric functions, or is there a fundamental difference?