Mea culpa.
I saw a very salient point in the comments--immediately following WWII, there was a public debt ratio of 105% of GDP, yet from 1945-1981 when we paid that debt down, we had 3.7% average GDP growth. Right now, our public debt ratio is in the mid-70s.
I find the use of "lies" twice in the beginning of the essay a hilarious rhetorical device, it's cheap but funny. Just wondering if anyone noticed it? How about you mk or flagamuffin? R&R are fighting a guy with a way bigger megaphone and are pretty much guaranteed to lose pop culture wise against Krugman, which is really too bad. Maybe it's not too bad actually, the arguments that R&R bring to bear in their letter aren't really arguments at all, I'd be slapped down in a moment if I had tried arguing from authority rather than theory in the classroom. R&R haven't proven anything, they aren't providing a theoretical argument more compelling than the opposition (does low growth create big debts or do big debts create low growth, the causality probably goes both ways).
I haven't been following this much since the original episode, but at least here, I think I have to agree with Krugman. In their letter R&R are basically defending the notion that a lot of debt is dangerous. However, I don't think that was ever at issue. The issue was that their paper erroneously made debt look historically more dangerous than it was. The whole problem was that they presented a distorted reality. It doesn't seem like they are willing to own that.
Looking back on it, and I think it was your argument that was most compelling, the problem is that R&R's data suggests a trend while their paper suggests an inflection point. Trends are guidelines. Inflection points are calls to action. One should not be confused with the other.