If you didn't have employers able to pay off the books and off the record safely in cash, you wouldn't have illegal immigration on nearly the scale that we do.
We all use cash in our everyday life, but we don't use hundred-dollar bills. We're not using 500-euro notes. And yet these account for mountains of cash out there. I think they're being used in tax evasion and by criminals of all types.
There has been a noticeable decline in the labor factor in all wealthy countries in the past 20 years. The rich are getting richer, but those at the lower end aren't moving ahead as quickly as the capitalists.