As an economist, I see a lot of over-simplistic economics 101 concepts being thrown around in the political debate about labor in the US. It is quite puzzling, even after many years in the profession.
Usually the fairy tale goes like this: let the market fix it. Most often, it won't.
Free markets are a very, very, very good thing. But they are not perfect mechanisms, and do not suffice by themselves in reality, because reality is much more complex than college level economics models.
Faith in free markets is a very good guiding principle, provided we also understand market failures and the need to address them. Otherwise we end up at equilibria that not only look and feel awful and morally unjust, but also suffer greatly in terms of economic results because of the terrible negative externalities generated.
This is why Scandinavian countries, with their oh-my-god horrendous tax pressures, extremely high minimum wages and large government programs are in fact at the very top of world's charts not only in quality of life and development indexes, but also productivity, innovation and GDP/capita.
People who struggle to make ends meet every single week do a poor job. They are not creative, they cannot afford risk-taking, they do not have time and resources to acquire new skills, they are emotionally upset, unhappy, prone to crime and social deviation. All things that not only make their life miserable, but also cost the society money because of their negative economic externalities generated by these situations.
The funniest thing, is that the country where more people think it's ok to let somebody who works 40 hr/week be poor is the country where it could be the easiest to fix this problem: the United States of America, with its tremendous pool of resources and talent; a lot of which are literally wasted to maintain some sort of bizarre faith in Introduction to Economics concepts.
Economic models are based on assumptions that greatly impact their results. Over-simplified models serve the purpose of explaining basic concepts in a clear way to people who do not yet have more complex instruments. They should not be used to claim anything outside of a basic economics class. That's what advanced economic analysis conducted at the frontier of research is for, and even then the results are often muddy and inconclusive.