Low Interest Rates and the Financial Crisis

Arjun Jayadev recently presented the following chart showing the effective interest rate for households and private non-financial corporations:
Jayadev was trying to dispel the notion that

the key cause of the financial turmoil in the U.S over the last two decades was the excessively low interest rates.

Attempting to reconcile this new data with my own views on recent economic history, I came to the conclusion that low incomes were a more likely cause of the financial troubles.

After providing my own analysis, a couple questions remain:

1) The data was calculated using interest payments from the household sector. Yet some interest payments are tax deductible, notably mortgage interest payments. Changes in tax policy that increase deductions or credits related to interest payments, thereby reducing the effective interest rate, may therefore not show up in this data. Is there a way to account for tax policy changes in regard to effective interest rates? How would this alter the above chart?

2) The effective interest rate as shown above does not appear to account for changes in credit quality. Given comparatively weak income growth and high debt-to-income ratios, I would argue that general credit quality was deteriorating over the past two decades. If that’s true, why weren’t effective interest rates higher in the past 20 years than during the 1950-1970 period?

My instinct is that accounting for tax policy changes and credit quality differences in the above chart would reflect comparatively lower effective interest rates during the last two decades. Contrary to Jayadev and Josh Mason’s work, this outcome would support the view that low interest rates were a cause of the financial turmoil. However, this result would not place the blame primarily on the Federal Reserve but rather on a confluence of actions from the government and non-government sectors. 

What are readers’ thoughts on these questions and/or my initial conclusion?