Oh man, "the left-brainers"? What happened to "Good design makes a product useful/understandable"? If it does either of those things, the effect would be measurable. I don't have any trouble believing that investing time getting the design right translates into better engagement or sales or whatever metric, and you should be able to hold your work up to the light. Writing off a provocative but genuine line of questioning such as jlarocco's is pretty much relegating yourself to the echo chamber.