Just because someone has a high income tax rate does not mean that the system is fundamentally unfair.
A progressive tax system would allocate the burden of the government on a pro-rata basis in regards to usage and ability to pay. Sales tax is a regressive system, which taxes almost everything. Coindicky, Massachusetts had one of the LOWEST if NOT LOWEST sales tax rate in the country. Most of the other states had local taxes and county taxes. Some people might pay 10% on bread and milk. In massachusetts you do not pay sales tax on food unlike every other state. In most states you are paying a high tax of 10% on food. I don't know about you, but I spend approximately 25% of my income on food. I worry about having kids to feed in the future.
One of these individuals in a high tax jurisdiction with a salary of 50,00 would suffer the equivalent of 2.5% income tax just for buying food. I am sorry. They are suffering right now. They have to buy clothes, too!
Sales tax favors the rich. It pays to be rich in places such as Florida, where you have no income tax. You pay less. You have no burden paying sales tax on your purchases as you do not buy more food then the next individual.
A fair tax or VAT would only see this rise to new heights in inequity.
Sales tax is also impossible to collect in entirety. It requires significant more personnel to police than an income tax system based on wage garnishment. Any nationalized system to collect tax on a transactional basis would require an organization considerably larger than the current IRS. It would require offices in many more locales in order to reach out to the public. The IRS currently has 100k employees. Each state government has at least 1,000 employees involved in collecting taxes, right now. I would think that a fair tax or vat would require at least 50k more employees on the federal level, but you also need more management to handle the new personnel and facilities. I also think that you need more employees to provide the coverage. Some states have very sparse employee counts.