> Noone parts with money for an exchange that they don't find useful.
I think this is true at face value, but when we consider addiction and self-destructive behaviors it is clear that while the definition of useful my still apply, the result is a negative impact on society.
The easiest most inflammatory example is drugs, but a more nuanced example might be slot machines. I won't wax lyrical about the examples, but I think they show that a transaction of money doesn't imply a positive impact on society.
Another example is rent seeking and fees, sometimes the transaction of money is non-negotiable, and one side is exploiting the other, or a middleman has inserted themselves (sometimes through policy lobbying) and extracts rent that no one benefits from but them.