As a private citizen no debt is generally the right way to go, but not always. It really depends on each situation.
A great example is buying a house. If you have the cash for the house that's great, but do you want want to tie up that much money into a single asset especially when the cost of money is so low right now? Other investments might not be that great today, but over the next 15 or 30 years you can probably find an investment that beats the current low rates of 3.75% or below.
The reason why buying a house is considered a good "investement" is because the government/federal reserve keeps creating more money and devaluing the dollar. Under such conditions, the person who borrows a lot of money now will do well. Homes are convenient for this because there is a lot of infrastructure/expertise in place to make this happen (mortgage industry), but the purchase of any large, permanent asset will work.
When you buy a house on credit now, you're spending newly created money. You're purchasing a large asset at current prices (which are set by the current money supply.) As the new money you've injected into the economy circulates, prices rise. But you had the advantage of buying before you injected the new money.
If money were not continually being created, eg if it were backed by gold, then prices would drop over time, because the rate of innovation and productivity gains is greater than the rate of new production of gold. In this scenario, houses should depreciate over time.
A great example is buying a house. If you have the cash for the house that's great, but do you want want to tie up that much money into a single asset especially when the cost of money is so low right now? Other investments might not be that great today, but over the next 15 or 30 years you can probably find an investment that beats the current low rates of 3.75% or below.