Industrial uses aside. I think people like diamonds because OTHER people like diamonds and because OTHER people consider diamonds superior.
I don't think it is really because of the brilliance, cut, or clarity because most of these qualities can be duplicated with cubic zirconia, etc.
This is the only explanation i've come up with that can explain why a young man would spend a large amount of money on a diamond ring for a fiance instead of getting an identical ring (or larger) of cubic zirconia.Chances are that neither the fiance nor her friends would notice a difference in diamonds and zirconia, but just to prevent appearing cheap, the young man opts to purchase the more expensive natural diamond.