I can only think of two occasions that you need credit money to invest:
1. you are in a war with another country, if you do not produce weapons fast enough, you will lose the war
2. you are extremely shortage on everything after a war that you need to reach a certain living standard quickly

But today is totally another picture: People take out a huge loan to buy a house, and that loan locked in their future income for 20 - 30 years. Due to this loan, banks become rich and start to spend big, economy get boosted. And after they finished their spending, economy start to shrink back, now even those people's future income for 20-30 years are threatened due to less consumption

If every investment is backed by enough saving, there won't be such problem. Housing is just like any other financial gamble game using high leverage. Many people are doing margin trading for house, that kind of risk is just too absurd, but thanks to credit money, every one can bet their life and play it