IMO, the path of Unity needs no defense, and is perfectly valid. However, the path of self-discovery, of power from within, seems to have long been repressed or denied by those who enjoy having power over others. The 'problem' with power from oneself is that no authority can be imposed upon it, and thus it is a threat to those who which to impose themselves on others. After discovering the Emerald Tablet at a website on alchemy , that philosophical construct seems as useful as any in the search to define and enhance the 'Adaptation' that is the self. Psychic development, for purposes of this paradigm, is the path of growth through understanding who and what that individual seeker is.
Spiritual development can also encourage growth, but is meant more to provide perspective.
The difference comes in more when defining what you are. The closest thing I have to a 'Bible' is Heinlein's Stranger in a Strange Land. It essentially accepts all religions as valid. This has been the basis for my philosophy since my early teens, though Taoism influences me greatly. I have recently returned to my 'roots' to explore this concept anew.