Income and capital gains should not be taxed at all.
US is more reliant on income tax than any other developed country. Over 50% of federal budget comes from income taxes, while in most European countries typically only 25-30%. That being said I figured if US implemented a 25% VAT they could scrap all income taxes, but that would probably be political suicide.The FairTax movement definitely supports this. It isn't exactly viewed as political suicide but it was mostly a 90s movement, although it got a bump with the Tea Party.