Let's make up some silly numbers.
Suppose the national debt was, let's say, 1,000% (ten times) annual GDP. And suppose the budget deficit was, let's say, 50% of GDP. And suppose your economy hit the Zero Lower Bound, and suppose you thought that your own central bank's monetary policy could do no more to increase aggregate demand, but more aggregate demand was needed.
1. Would those numbers lead you to hesitate before recommending tax cuts or increased government spending to increase aggregate demand?
2. If I divided both those numbers by fifty, would you still hesitate?
If you answered "yes" to the first question, the punchline writes itself: we have already established that you are an austerian; we are just haggling over the price.
I'm not looking for some sharp dividing line, because I don't think there is one. (There is nothing magic about a 100% debt/GDP ratio, for example, because if we measured time in months instead of years, 100% debt/GDP [edit: monthly] would become 8.333% debt/GDP [edit: annually], and 8.333 doesn't look like a magic number.) But I am looking for some sort of recognition that there's some sort of convex trade-off, or increasing marginal costs of debts and deficits. And the slope and curvature of that trade-off, or the height and steepness of that marginal cost curve, may not be easy to estimate accurately.
Is the difference between "austerians", and those who accuse others of being "austerians", merely a matter of degree?
I think it is.
Worthwhile Canadian Initiative 
Nick
“But I am looking for some sort of recognition that there’s some sort of convex trade-off, or increasing marginal costs of debts and deficits.”
Total interest paid in any annual period = Total Debt * ( 1 + Term Premium * Short Term Interest Rate ) ^ Average Duration / Average Duration
Let the term premium be some multiple (alpha) of the natural log of the average duration:
Term Premium (TP) = alpha * ln (Average Duration)
For any combination of alpha and short term interest rate, there is a sweet spot non-zero average duration that results in the lowest amount of annual interest being paid.
For instance let the short term interest rate = 1%, and alpha = 0.5.
The least amount of annual interest will be paid when the average duration of government debt is about 43 years.
A couple of other calculations:
ST INT% = 5%, Alpha = 0.5, Sweet spot duration = 12 years
ST INT% = 1%, Alpha = 0.75, Sweet spot duration = 31 years
ST INT% = 5%, Alpha = 0.75, Sweet sport duration = 9 years
In using the term “average duration”, I am thinking that the government issues all the same duration of bond with 1 / average duration bonds coming due every year (accrued interest is paid from tax revenue, principle is rolled over). If government is using coupon securities, then interest payments on all debt come due every year and there is no benefit to extending duration.
Ugh,
Just realized my mistake.
For any combination of alpha and short term interest rate, there is a sweet spot non-zero average duration that results in the lowest amount of annual interest AND principle being repaid. Interest only would be:
Total Debt * ( ( 1 + Term Premium * Short Term Interest Rate ) ^ Average Duration) – 1 ) / Average Duration
Is rollover a choice or is it coerced? If rollover is completely a choice, then the term premium should be stable with a stable average duration. If it is coerced, then the term premium can become unstable. The numbers above apply to the minimum annual interest and principle repaid every year as a percentage of total debt.
For instance, with a short term interest rate of 1% and an alpha of 0.5, the government would pay out about 2.85% of total debt in interest and principle repayments ever year. To get a sustainable debt to GDP ratio of 1000% with government collecting 15% of GDP in tax payments, it would need to reduce its interest and principle repayments to about 1.5% of total debt (15% / 1000%) – here all tax collections would go towards debt payments. Assuming a constant alpha of 0.5, the short term interest rate would need to be at about 0.6%.