By implication, this means the "services" (for lack of a better word) provided by the bad bankers are, in aggregate, worth much less than zero -- meaning the massive overt harm committed by these serial criminals makes their work much worse than merely "worthless."
Even more generally, we have an entire industry -- investment banking -- that extracts exorbitant fees for its services (the largest in the history of human commerce); but where even the friends of this industry explicitly point out (via long-term data) that these services are absolutely worthless.
There is an identical parallel in nature. Creatures that relentlessly suck the blood from other creatures while providing nothing in return are known as parasites. Those are the "good" bankers.
For an appropriate analogy for the bad bankers (i.e., the traders) who relentlessly blood-suck their "clients" while simultaneously doing massive/catastrophic harm, there's