Your comedian wasn't funny.
Subject: 4% interest rates for 20 years???? Your comedian wasn't funny.
It doesn't matter whether Prof. Galbraith is right about interest rates remaining at 4% for 20 years (like drawing 10 blackjacks in a row in Vegas. -- OK, 20), it's the "off balance sheet" unfunded liabilities that everyone so glibly dismisses with a single sentence.
The minimum estimates of the cost of those (Social "Security" and Medicare -- before Obamacare) was somewhere around $66 trillion.
The debt clock currently shows them at about $108 trillion.
Health, happiness, & long life,
L. Reichard White
P.S. OK, like drawing 100 blackjacks in a row. And as Prof. Galbraith suggested in a backhanded manner with his "U.S. controls its currency" comment, inflation is the nearly inevitable outcome.