It's clearly unsustainable. Eventually it leads to a run on the dollar and inability to refinance the debt. At that point, the debt gets inflated away.
I ask you: do you imagine it can continue forever, with debt reaching arbitrarily high multiples of GDP?
I agree that the system can become unstable. Clearly; it's being made unstable currently.
I disagree that it must become unstable, especially on a time frame relevant to anyone currently alive. Perhaps certain resources could be sheparded more sustainably than they have been but I do not think we were previously heading towards a consequence worse than we are currently experiencing.
That argument applied to current administrative actions is like saying "we all die someday, therefore we should all commit suicide right now".