That poster was obviously written by someone who does not understand or like businesses or entrepreneurship, and has never started a business on their own.
One of the main goals of forming a corporation is to protect the people who own it from legal liability and debt.
Meaning, if you work for, or own, a business, say "THE plumbing corp." (referred to from here on out as "TPC") and one day TPC does something harmful, such as install faulty piping either knowingly or unknowingly, people can sue TPC, but cannot seize The's or The's employees' personal assets, such as their home and savings. Most people starting businesses or working for businesses want some protection from this kind of liability. It is possible to lose your home and all your savings if your company is structured differently, for example, as a sole proprietorship. Incorporating is not at all the only way to structure a business, though.
Here's a definition of a corporation from Investopedia:
A legal entity that is separate and distinct from its owners. Corporations enjoy most of the rights and responsibilities that an individual possesses; that is, a corporation has the right to enter into contracts, loan and borrow money, sue and be sued, hire employees, own assets and pay taxes.
The most important aspect of a corporation is limited liability. That is, shareholders have the right to participate in the profits, through dividends and/or the appreciation of stock, but are not held personally liable for the company's debts.
Corporations are often called "C Corporations."
Businesses, including corporations,
are made up of and started by people, I said that once to you, I remember.
P.S. And to clarify, a baby cannot be a corporation,
and be stock,
and be used as collateral. They are three different things. (Well, four, technically.)
P.P.S. And national debt is also a different thing. I have no idea if countries' loans are capped based on population size. But I don't believe they are.