Suppose that there is one principal employers in an area, the other having recently closed its doors leaving many destitute - some practically living under bridges, and for this example there is no such thing as welfare.
Those living under bridges, the former employees, of the employer who went under - are keeping themselves warm by means of cardboard box shelter, keeping themselves by by the nature of the very bridge itself.
The employees of the remaining company are making $7.50 an hour. That company's owner decides its too much and promptly fires his employees when he discovers that those living under the bridges are willing to work for $2.00.
So now we have the under bridge dwellers - who are able to scrape by and afford a little beans and rice, while still living under the bridge. And we have the ex-employees who are looking for a bridge of their own, as there are no other jobs available and they are now making NO money.
The problem with NOT having a minimum wage is that unscrupulous employers ARE given far too much power in limited job markets. The employee is one of thousands, so he is forced to take a menial wage of simply survival - because there is always some else so desperate to survive that he might be willing to take a few cents less. Whereas employees have only one (in this case as an extreme) company to bargain with. If they choose not to take the job there MAY not always be unlimited opportunities to work elsewhere as suggested in the cartoon.
The wealthy can always collude to make sure that they offer not-even-subsistence wages if allowed to do so. But the individual employee has only one choice - to work and eat or die.
Sweatshops, indentured servants, slaves and serfs are ALL products of putting all wage decisions into the hands of the employers who become very powerful while those who actually work have no bargaining power whatsoever.
Is THAT what you want? All power in the hands of a few wealthy?
What you are suggesting about pure supply and demand labor markets SOUNDS great, if there are plenty of employers, plenty of employees, and the company owners do not collude. Its a great model. But it doesn't always reflect reality.
Reminds me a little bit of the glowing promises proponents of communism make. Everybody will contribute to the best of their abilities and everyone will be reward according to need. Sounds idyllic and many people are fooled by the simple great sounding model. The problem is of course that people DON'T work as hard as they can, people take advantage of the system and in real life human nature makes it certain that communism will NEVER work.
Idyllic ideas, are just that...idyllic. But they don't reflect greed and the real world.