system
Given the following post, respond as if you're commenting on Reddit:
human
What are the strongest arguments against a flat tax?

I was arguing with a good friend about whether America should switch to a flat tax. I am opposed to a flat tax because it would place more tax burden on the middle and lower classes.  My friend, however, laid out a pretty convincing argument based on fairness.  He argued that there is no reason why a wealthy person should pay a greater % of their income in taxes.  Are there other arguments against flat taxes out there?
gpt
Almost no matter how you structure a flat tax it is regressive, as you point out. That makes it "unfair" for the poor by forcing them to make greater sacrifices to pay tax that the wealthy.

There is no way to create a perfectly "neutral" tax system, mostly because people can't agree on how to judge the tax system. If everyone pays a flat 20% of their income, those making $200,000 have to sacrifice mush less than those making $20,000. But if the person making $200,000 pays a higher percentage, that is also "unfair."

The basic reason why all industrial economies have a progressive rather than flat tax is practicality. A family of 4 making $20,000 are barely surviving, asking them for a 20% tax would make life much harder for them. It then becomes harder for that family to get out of poverty because they can barely cover food and rent. However a wealthy family of 4 making $200,000 will not be as greatly impacted. Their ability to pay food and rent is not at threat, even if the rent is not at a place as nice as they would like. They can afford more because they have more. Basics of life are a much smaller percentage of their income, so taxes are much less disruptive to them. 

The US tax rate is 22% of GDP, the lowest in the first world by several percentage points. Even still, if all people had to pay 22% it would make life much harder for the poor, increase demand for government assistance programs, and extend the wealth disparity which suppresses demand (as there is less people with disposable income). Taxing the very poor then is bad for the economy and expands poverty by removing thousands of dollars that otherwise would have gone to basics. But the price of taxing the poor less is you have to tax the wealthy more to maintain that average. If you want families making $20,000 to pay few taxes, people making $200,000 will have to make up the difference.

Now that is for a flat income tax. It's basically an argument of practicality and poverty elimination which is admittedly not as principled an argument, but it is more well demonstrated rather than theoretical and has worked for over a century. However if (like many) he is talking about a flat *sales* tax, that is a different story.

A flat sales tax is even more regressive than a flat income tax. Going back to the two families at $20k and $200k, they both have four members and therefore only have four mouths to feed and bodies to cloth. Obviously the quality will be different, but there is a limit to how much is needed per person. The second family will spend more money than the first, and therefore pay more tax, but the money they spend on taxable items will be a smaller percentage of their income. This is not theory but imperical, those of great wealth, particularly those making a million or more, spend a much smaller portion of money in stores in the US. So the poor family that live paycheck to paychek will have almost all of their money go to taxes where as a wealthy family would have a much smaller percentage.

Additionally, at least in the US, a flat sales tax would a huge power grab by the federal government in what is normally considered a state matter. Sales tax has historically been set on a state by state basis, some state having no sales tax at all. States like having this power and so would fight hard to stop any federal unilateralism. And the party that usually sides with the states (Republicans) are also the party more likely to support a flat tax, so you will see an odd coalition of state's rights Republicans and most if not all Democrats opposing such a plan. It would politically be nearly impossible to implement in the US.