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In Wealth of Nations and other works, Adam Smith pointed out that essentially the only way that workers could participate fairly in a capitalist system would be to form unions. Adam Smith, the supposed darling of capitalists, actually favored labor unions. Otherwise all employees would inevitably have the status and economic power of slaves. That's how it was in the 19th century. Dickens' best novels are basically horror stories about brutal British labor conditions. Hence the word "Dickensian".
In the US, the enabling legislation was passed under the New Deal. Before that, unions were practically illegal. The middle class in the US was very small before the 1950's.
For most of human history society was characterized by a small wealthy ruling class dominating the much larger impoverished and disempowered masses. That's the historical model. The present period of relative middle-class prosperity is widely considered to be an aberration of history. Ultimately the goal of union-busting and other tactics is to re-establish the historical model.