First, lets do extreme examples to showcase the problem. Lets say that 70% of the income of the poorest people pays for taxes, the richest pay nothing. The poorest people are more numerous, but without enough income to rise up through their society there are few threats to those at the top. In nature the kiwi bird lived in an environment with no predators, it lost all the size related traits its lineage came from, because in a world built on scarcity of resources, weakness isn't a problem life cares about, it only cares about survival, a species could lose everything so long as it continues to reproduce.

So, without competition the ones at the top of society are weakened, and the majority of society suffers because to improve their lives is to threaten the structure of their society. It is harder to control people who have access to things like healthcare, education, freedom to travel, freedom to speak their mind, freedom to do work. By extracting resources from the poorest people, society stagnates or at least grows very slowly.

If we crank the tax up to 100%, the poorest people die out in prisons if they survive somehow, or they die after giving everything up. But once they are gone there's a new poorest segment of society, and this repeats until there's only one person left. This might be a faster process, but all regressive tax systems, including tariffs, will whittle away at the wealth of everyone over time.

People buy things, that's what makes the economy work. If people can't afford to buy things, the economy slows down. If people have no money, the economy stops. Sure, you might own a fancy car you could sell if times are tough, but what is it worth if you can't find anyone that wants to buy a used car? Suddenly all these things people own or produce has no value because nobody has the money to buy it. They might want it, but all they have is stuff. So as more of the economy freezes, the people making the money at the top find that the only people buying things is other people in their social class, and those people aren't producing anything, they own things. They might pay people wages, but those wages are swallowed up by taxes, almost none of that buys things from the companies the people at the top own.


Then there's progressive taxes. Again, lets do the extreme and have the poorest people pay no income taxes, but the people at the top pay 70% of their income in taxes. Since it's popular now for the richest people to be paid in shares and a $1 annual income, and they buy companies using the projected increase of value of those stocks over time without ever selling those stocks, this income tax would need to account for this loophole, perhaps 70% of stocks that replace their wages goes to the government.

Since there's a cutoff between who counts as rich and poor, the rich who are near that line might choose to not receive a million dollars (or equivalent) a year, and instead put that money into the business, or their workers wages if they can't spend it on anything to grow the business. More wages attracts better employees, but it also means people spending more money on things, which speeds up the economy. If people buy more things then companies make more profit leading to more wage increases. Eventually people might satisfy their need for things and society might plateau at this economic peak, but over time more people will go from poverty into middle class wealth for a long while, it could take a long time for everyone in the world to become a consumer.

And remember, the people paying these taxes are still millionaires, they won't be starving in a progressive tax system, and this doesn't hamper business growth, so even though their wages are stagnating compared to the rest of society, they likely wouldn't change their lifestyle much even if their income went up 10x.

A regressive tax system is pretty flat, because their economy doesn't grow much. With most of their wages going to taxes, and people spending only 30% of their earnings on themselves, the poorest citizens live from day to day and so can't afford to improve the world. In such a society, only 6.6% of the population is able to afford the time to improve society as a whole. In a progressive tax system, given enough time for it to work, 100% of the population is able to afford the time to improve society. Even in the worst case scenario a person earning a million dollars a year is earning 300k a year, and most rich people would put off increasing their wages until they are guaranteed more than a million dollars after taxes.

Another thing to note is elections. Elections are a system where the majority decide the direction their country is taking, and the richest people in the nation are a minority. They can own news stations and they can pay to support politicians, but there isn't anything they can do to make their vote count as more important than any other vote. It's in their best interest to make people who oppose them not want to vote. Maybe transportation is lousy, maybe it's too far away, maybe they run ads that confuse people on when and who to vote for, but the goal is generally the same, turn their money into votes somehow. In a regressive society there are no votes, or fixed votes, there's nobility and oligarchs and that's about it. In a progressive society there's more incentive to vote because there's more encouragement to participate in politics and business in general, because the richer the society is the more money the government makes.

And a thing to remember is that government income comes from taxes, if the rich aren't paying them then the poor is paying it instead. If taxes aren't paying for healthcare then you're paying companies for it or going without healthcare at all. Some people might think that if they don't use something then they shouldn't have to pay for its availability, but I have an example that disproves that point.

Insurance companies have been pulling out of wildfire prone areas, because they are happening more regularly, and insurance is like a lottery, you are betting your home burns down and hoping you are wrong. The problem is that if it's likely to happen in an area, then they have to pay out, even if your personal odds are low, for them it's guaranteed every year. The business model fails, so they pull out, there is no insurance, or what exists isn't going to cover the current cost of a home.

Your quality of life depends on the lives of the whole country. The better off everyone else is, the better your own life is, even if you're paying for things your neighbors use but you don't. This is why roads are paid with taxes, even if the corporations are the ones making the most from it, everyone is able to use them because limiting access would slow the economy in a progressive society. Regressive societies have roads the leader uses to reach their airport, and that's about it, because that's how regressive societies maximize their profits.