Debt is a tool. Like margin investing. He sounds like a Great Depression survivor.
His was useful advice when the US had a gold-standard, and we did not have a completely printed, fiat monetary system, with government debt as the main asset underpinning our financial system.
Now we live in an era of printed money and baked-in, guaranteed inflation. If you can buy an asset that produces dividends or returns greater than the politically manipulated interest rate, then it makes sense.
That's why most physics and computer science PhD's wind up in finance. Its become an arms race, and Wall Street and Washington DC is absolutely guaranteed to do better than the average American citizen.