Naturalism" seems to me in this and other respects rather like "World Peace." Almost everyone swears allegiance to it, and is willing to march under its banner. But disputes can still break out about what it is appropriate or acceptable to do in the name of that slogan. And like world peace, once you start specifying concretely exactly what it involves and how to achieve it, it becomes increasingly difficult to reach and to sustain a consistent and exclusive "naturalism." There is pressure on the one hand to include more and more within your conception of "nature," so it loses its definiteness and restrictiveness. Or, if the conception is kept fixed and restrictive, there is pressure on the other hand to distort or even deny the very  phenomena that a naturalistic study — and especially a naturalistic study of human beings — is supposed to explain.