Japan is actually the largest, fwiw. These Fed programs are being financed by debt spending, not tax increases. So even if some of this debt is held by US tax payers, it's not at their expense. They're getting paid interest.
Yes, well actually if the economy grows at all, a constant tax rate brings in more revenue, while we tend to spend more too. But I agree it is theoretically possible.
Except that the Fed is buying bonds that pay a higher rate that they borrow at (U.S. Treasury rate). So unless there is a lot of defaulting, they should be fine.
It's like they are mortgaging the White House at 0.25% and buying bonds that pay 4%.