"Diversity of thought" is a right wing/reactionary pseudo-centrist euphemism which prioritizes the inclusion of bigoted perspectives over actually giving any weight to the concerns of previously-excluded voices and groups. It is a rather loaded phrase... though perhaps that's what you're aiming for?
Perhaps the person you asked this question might answer your rather political & insulting presumptions about the author's motive of "actually" ignoring any other viewpoints except his own? However, perhaps I might quote from a different book by Rudolf Steiner which contained this rather relevant advice in the context of your question? : "Always consider the possibility that you may be wrong." If those who have clearly formed a cult around his literary output would approach other people's different philosophical ideas, and question any such fixed ideas of their own, then perhaps they would have accepted his suggestion that the Anthroposophical Society ought to change its title, on a regular basis and read whatever other spiritual scientists or occultists have to add to his philosophy of freedom. i.e. the only freedom I suggest is worth having is the freedom to be oneself and completely detached, rather than fanatically identifying oneself with somebody else's philosophy, or one's own, in a one-sided way. Perhaps that's what you're not aiming for?!
