Gents -
I put it this way. Imagine if Nature, besides providing the raw material for a golf course, also decided one day to create an actual golf course - fairways, greens, tees, hazards, an entire, usable field of play. What would that golf course look like? What qualities and properties of Nature itself would Nature itself choose to manifest if it was required to design a setting for golf? Whatever you think the answer is, I think THAT would be the definition of natural design, and a description of naturalism. And I think that anyone - Mackenzie, Behr, Tillinghast etc -- who talked about natural design was talking about the hand/works of man getting as close to this Ideal as possible. Why? Maybe if for no other reason precisely BECAUSE it was the Ideal, and because of the inherent worth of striving for such an Ideal. But I think there may have been other reasons too, more subtle ones. Behr I think was grappling with understanding/explaining why the few golf courses that approached this Ideal resonated with him so deeply. In other words, he was trying to understand and explain HIMSELF through the medium of his experiences on the golf course; and then to work outwards from that self-understanding to establishing the principles of a golf course architecture that might best and most completely satisfy his human nature, and human nature in general. Sometimes I think he was a fool for trying to do that; much more often, though, I tip my hat to him for the effort -- not IN SPITE of the fact that the effort was doomed to failure, but BECAUSE of it.
Peter