Economics for simple Minds - Unions are bad for Growth (Stelzer)

Economics is not an exact science, if it is a science at all. For that reason ideological prejudices are often hidden in simple statements such as this one: 'A Union revival that will hurt Growth' (Irwin Stelzer, The Weekly Standard). 
Unions may well have created all sort of economic and political havoc but before one makes the statement one should first check the facts: was economic growth really slower when union 'power' was higher? And what about the distribution of the growth? What is growth worth if only a very small minority benefits - today's equivalent of the Robber Barons and their hangers-on?