The US debt is a problem in the same way that the earth constantly falling into the sun is a problem. You've missed a velocity vector in your analysis. Ask yourself this: if you get dollars for your maturing Treasury, where do those dollars end up in aggregate? They are either taxed away due to them circulating past tax points as they are spent and respent, which eliminates the need for a bond, or they are saved whic…
The solar system is an extremely stable system, while our economic system is not at all stable.
Your proposed money cycle is based on the concept of a closed system, which the US economy is definitely not.
If the US government starts having to pay an unbearable amount of debt, money is going to outflow to other countries and make it harder for the US to issue new debt.
If the US just issues enough money to pay the debt off, then interest rates are going to go through the roof and overcompensate for what just happened, making the situation even worse. The US economy would probably collapse.