The billionaire investor Paul Graham has a theory about unions. Union membership, according to Graham, expanded in influence and size in the growing manufacturing sector during the late 19th and early 20th Centuries because the sector treated skilled workers who could turn metal into cars using their hands and their tools as the scarcest resource out there. That meant workers’ demands had to be met, and more importantly, could be met easily from ever increasing profits. So demands for unionisation were simply met and passed on as a cost of doing business in a growing sector of the economy.  In…