Hyperinflation in the Weimar Republic led to civil unrest and ultimately to WWII anyway. Perhaps the same cycle could repeat itself in the future.
You see, under a default the people who lent money to the US government get wiped out.
But under hyperinflation, everyone who holds US dollars could get wiped out whether they lent to the government or not. Paying back creditors with hyper-inflated dollars is essentially the same thing as a default and will anger both foreign creditors and domestic creditors anyway:
Thus although, a Default could theoretically lead to unrest and world war III, the same is true of hyperinflation. The real question is do you want lots of angry rich people/investors and foreign creditors or do you want everyone who holds dollars to be angry including the creditors?
Perhaps, but Weimar in 1923 was still a conquered nation with no control over fiscal policy.
That is far from the situation that the US confronts.