There is a counterparty to every financial transaction. Presumably, both sides are happy if they agree to trade with each other. All of what you call "unproductive financial schemes" are mostly about exchanging risks, just like insurance.
Any conman worth his salt can sell a lemon, a toxic financial product or snake oil.
In UK naive homebuyers bought leaseholds where service charge and ground rent increased EXPONENTIALLY every 10 years. They even had lawyers, and those greenlit the deal.
Or when banks handed loans to strippers and then sold the loan to 'investors' causing subprime mortgage loan crisis of 2008. S&P were meant to do due dilligence, the 'sophisticated investors' were meant to do due dilligence, but here we are
