Final answer:
Mortgage debt was considered a good investment before the 2000s due to rising home prices and the securitization process, which allowed lenders to sell the risk to investors. However, overly lenient credit ratings and a downturn in housing prices led to the financial instability that resulted in the Great Recession.
Step-by-step explanation:
Prior to the 2000s, mortgage debt was considered a good investment because home prices were generally increasing. This meant that even if borrowers defaulted on their loans, lenders could still potentially sell the property for a profit. Lenders mitigated risk by using a process called securitizing, where they sold mortgages to financial entities that created mortgage-backed securities (MBS) and sold them to investors. Investors found MBS appealing as they provided a steady income stream, as long as borrowers kept up with their mortgage payments. However, the rating agencies were often too lenient in assessing credit risk, and when housing prices fell, investors and banks faced significant financial challenges, contributing to the Great Recession.