There are several studies, notably by Reinhart and Rogoff that indicate when a country's debt to GDP ratio approaches 90% that economic growth is adversely effected. A default usually occurs if insufficient action is not taken to reduce the debt load. Nobody, and I mean NOBODY, has ever spent their way out of a debt overhang and into prosperity. Spending generally results in a temporary boost, the effects depend on the efficacy of the spending; the problem is that it's temporary. When the extra spending stops, so does the growth.
You're drawing really broad conclusions from Reinhart and Rogoff that their data doesn't really support. They acknowledge that their data set for GDP/debt ratios north of 90% are not very common. Furthermore, the claims of danger are built on the idea that the bond market will demand higher and higher interest rates after crossing the "threshold". Reinhart rejected that idea, pointing to Japan.
No better example exists than right here over the past 3.5 years. Look how much extra spending has occurred since 2008 and TARP. and a tax rebate. We lowered the prime interest rate down to nearly nothing, and what do we have to show for it? 1.9% growth in Q1 2012, many project about 2% for the year.
Versus the likely counter-factual of zero.
They didn't reject the idea, based on only the Japan case. They did note there are extenuating circumstances peculiar to Japan. But it's true that Japan has been the exception to the rule, their debt to GDP ratio is way up there but they're still doing okay and the bond market has not hurt them much. And it's probably fair to say that there are other factors that can subdue economic growth or mitigate it. But it's also true that R&R's research does show a correlation:
" the relationship between government debt and real GDP growth is weak for debt/GDP ratios below a threshold of 90% of GDP. Above 90%, median growth rates fall by 1%, and average growth falls considerably more. "
A Decade of Debt, Carmen M. Reinhart and Kenneth S. Rogoff, 2011
In their study, they said that 92% of the cases were under the 90% threshold for the ratio, over the past 200 years or so. Since they examined over 1300 cases, the number is not insignificant IMHO. Only 2 cases exceeded the 120% threshold, Japan and Britain from 1946-1950.