Unions came about at a time when the power to decide the circumstances and conditions under which employees worked rested almost entirely in the hands of the upper management and owners of the Industrial Revolution. As with any human population, that group its range of ethical and humanitarian values, but many of the most powerful were men like the ruthless Henry Frick, hired by Andrew Carnegie who saw himself as something of a softie and needed someone more aggressive. He didn't realize just how aggressive until later..
Unions succeeded in empowering labor and gaining some balance between employers and employees. But power corrupts, and as unions grew in power, they did as so many have, relished it and sought more, beyond their mission