An assumption can be widely held even if most informed people would dispute it. For example the widely held belief that housing prices will only go up, despite historical and theoretical arguments to the contrary.
That is absolutely true. I guess my incredulousness stems from that I would consider myself rather uninformed about diamonds and other gemstones, and still I have found the future of the diamond business very questionable. Basically since I saw some movie about how they are kept in stockpiles, and also the movie Blood Diamond. I would have thought it to be rather mainstream knowledge.
I don't think that's the sense in which the article stated it. It seems to me like there might be a significant number of people in the industry that believed it.
