Earlier quoted context omitted.
My job is completely detached from the processes and people that ensure there is food on my table. There is no slack to pick up because there is no contribution. Most software developers are in the exact same position. There is no "contributing" in programming casino sites, optimizing trading algorithms to make fat cats richer, or developing aaa games. Society would be better off if we didn't work.
Programming casino sites has value because people choose to spend the money that they earn gambling. Society decides which tasks have value and which don’t by whether consumers spend money on the work product produced by those tasks. Now, society’s way of working this out isn’t perfect, but how else should we determine which jobs are adding value and which are not?
You ask how we should decide what jobs has "value" and which hasn't. Well, if it isn't obvious that a job has "value" then perhaps it has no value?