Do you think small businesses that are "cash-intensive" (a business that receives a significant amount of receipts in cash) such as restaurants are bad and should not exist?

Statistically speaking that is the kind of business that the money launderers use to launder their dirty money. But nobody can say these businesses are bad and should not exist because that is not their utility. It is the same with bitcoin mixers. When blockchain analysis companies came to existence with the sole objective of invading people's privacy and to surveil, obviously there should be a tool to counter them which is when mixers come in to provide people with that additional privacy.

Because of the nature of mixers (similar to nature of cash intensive businesses) they will also be used by criminals, which is unfortunate but we can't do anything about it.