"The maxim by which I propose acting is that of acting to maximize expected utility. If everyone does this then perhaps 1000 people will buy drugs from a criminal organization and hence enable it to commit a few more murders -- but they will only do that if the good each of them is able to do by buying those drugs outweighs the (incremental) harm caused by their contribution to the criminal organization, in which case collectively they will do enough good to outweigh those extra murders. I am happy to live in a society that makes such tradeoffs."

YES

"he's argued that getting such a job would do less good than earning a lot of money and giving much of it away."

YES the value being the difference between if the organization hired you compared to their next best alternative.