The oldest comment regarding public debt and its sustainability that I have seen personally is in Adam Smith’s Wealth of Nations. In the work published in 1776, Adam marveled at Great Britain’s indebtedness, but also noted how throughout the 1700s, expectations that unsustainable debt would backfire had not come true.
Yes, at some point the limit will be reached, but apparently in Britain this limit has been speculated on for 300 years now. 
One person’s debt is also another person’s wealth, so if you complain about over-indebtedness, you are complaining about excessive wealth. 
Perhaps there is surprisingly a lot of debt capacity to be found on this planet after all…