When businesses became involved speculation in the derivatives market it was not much different than if they were out-and=out gambling. Suppose businesses began to bet heavily on the Kentucky Derby. Imagine GM placing a $500 million bet on the Derby and Microsoft risking $100 million and so on. Then on Derby day there might be some major companies that would go broke as a result of their gambling losses. Others might be rolling in money. There could be a financial crisis on Derby day if Wells Fargo and the Bank of America and so forth bet the wrong way. Blaming the financial crisis of 2008 on CDS's would be like blaming a Derby Day crisis in the hypothetical situation described above on the Kentucky Derby. The problem was not the instruments but instead the businesses being heavily involved in gambling.
Instead of a hypothetical case consider what happened when American businesses in the 1980's found that they were subject to a risk due to their dealing in foreign transactions. Typically in foreign transactions there are gaps between when a sales contract is entered into and when the money appears in their accounts in dollars. Some companies set up divisions to handle the the transaction risk and made many millions of dollars in speculation in the foreign currency markets. Others were cautious and immediately sold the future foreign currency payments for dollars now. Those that speculated found to their sorrow that a huge profit in one year did not mean that they could count on profits in subsequent years. Many incurred solvency threatening losses in their foreign currency speculation. The full story is told at Transaction Risk.