This is such an important point that so many seem to miss. The more income you have, the higher your disposable income. A person who earns $20k per year probably spends $20k per year. A person who earns $50 million a year isn't going to spend $50 million every year. Even if their income skyrockets to $150 million, they likely aren't going to spend $50 million in a year. It's just not feasible. Therefore, any sort of FairTax or FlatTax is hitting the poor a lot more than the rich and is regressive by definition.