Really! Getting lots of other people to take on debt results in many other people making immediate profits to the short term benefit of all.
Consider. We get Sally to take out a large mortgage on her home. The person issuing the mortgage takes the mortgage, sells it to an investment bank, and makes an immediate profit. At the investment bank they take those loans (small investments with considerable risk), bundle them into a deal, and slice and dice off several (rated) safe tranches that they sell for a profit. The purchasers of said debt get to take money that wasn't making interest and put it into something that makes money, resulting in an immediate profit on the books.
All of those companies along the way record profits, and pay generous bonuses to the people who did those things. Those bonuses are a profit to the individual that is kept whether or not the organization runs into future problems. Which creates perverse incentives. There were many individuals who realized that they were doing something unsustainable. But if you don't do it, you'd lose your cushy job, while if you do it you make nice bonuses. From their point of view the possible eventual failure of Lehman etc were externalities and they were motivated by their current bonuses.
Furthermore back in the neighborhood, Sally didn't sit on her money. Instead she spent it. The various businesses she spent money at get to record profits on those sales, which in turn goes to hiring people, paying healthcare premiums, etc.
None of that would happen if Sally didn't take out that mortgage.
In short what has happened is that the taking on the debt results in causing money to circulate. As money circulates, multiple people record profits. This is well understand, and is why standard macro-economic theory says that money is effectively created when debt is taken on. And, on the whole, this is a good thing.
The problem, of course, is that just as money gets created by the taking on of debts, money gets destroyed when debts are abandoned. And when people take on debts they can't afford, they do get abandoned. Which is the current problem we are dealing with right now.
