Remember that pre-1900 rates of 2 - 4% were common. In WW2 in 1944, the top bracket was 94%. War is ridonculously expensive. Many caveats, but if 0% is not an option we should all want to see 1.5% rather than 15%.

15% still incentivises the use of accountants, inefficient reporting & corporate structures to shield themselves from paying. Sounds utopian, but the world would likely be a lot more peaceful and productive if it were single or decimal digits. People & companies would just pay and get on with building cool stuff.

Close the loopholes a 15% flat tax makes sense.

But I think the tax should be a consumption tax on goods and services. Yeah it will suck for producers and consumers but if you grow your own food and make your own products then you would never pay tax. But getting rid of income tax all together will instantly boost productivity and not punish high earners for producing.

People living in western nations if you don’t want to pay taxes you can leave. Denounce your citizenship leave the country set up shop somewhere and make it happen. You have the option to leave and be a free human on this planet but most would die in a week without modern amenities. Even those Alaskan bush people go to town to get goods services and Mates so they can breed.