Returns to rentiers are simply inefficient, because funding can in fact come from other productive stakeholders. This is the Cooperative Advantage of a Not for Loss "Social Business" model as Dr Yunus calls it.
I think current capitalism is about to be hoist by its own petard. The mechanism will be the pervasive spread of P2P Finance, and there will be a transition from banking as credit intermediation to banking as service provision. "Any economic unit can emit money. The serious problem is to get it accepted" Hyman Minsky