Most of the time that I see people invoke "Econ 101" concepts, they are wrong. Supply and demand does not account for the power imbalance between workers and leadership, which unions specifically attempt to address. It does not account for the class differences between workers trying to make ends meet and the board of directors who believe they deserve much higher pay than workers. We are free to change the perceived value of workers through the power of worker solidarity - ensuring that individual workers are not so easily replaced to keep wages suppressed. You can simply say "it's supply and demand" and do nothing to support the workers whose labor is so clearly needed for our economy to function, or we can support collective bargaining rights to make sure that individual workers are not crushed under the power of company leadership. How you view this is up to you, and not a simple fact of natural laws of economics.