"The biggest objection is that important programs will be underfunded. But that consequence is actually logically impossible. If Americans don't think a program is important enough to provide more funding, then in a democracy, by definition it isn't a priority so doesn't deserve more funding. I also think you would be surprised at how much money Americans would choose to provide to entitlements. More Americans might want contribute money to Social Security and less to the wars in Iraq and Afghanistan, for example, because they might prefer to provide for the retirement of Americans instead of bombs in the Middle East."
https://www.theatlantic.com/business/archive/2010/10/what-if-taxpayers-could-decide-how-their-money-is-spent/63946/
https://www.theatlantic.com/business/archive/2010/10/what-if-taxpayers-could-decide-how-their-money-is-spent/63946/