…from Herbert Spencer.
As a balance of power:
“Everywhere aggression begets resistance and counter-aggression; and in our present transitional state, semi-militant and semi-industrial, trespasses have to be kept in check by the fear of retaliatory trespasses.”
Generations later, we’re still in that transitional state. There are other justifications, of course, but Spencer correctly sees that organized labor is, essentially, defensive.