Earning to Give on Wall Street: more harm than good?

A couple of years ago, William MacAskill wrote a post explaining that it was better to get a job on Wall Street - and give away a large fraction of the earnings to charity - than to work for the charity itself.

http://qz.com/57254/to-save-the-world-dont-get-a-job-at-a-charity-go-work-on-wall-street/

He's since back-pedalled:

https://80000hours.org/2015/07/80000-hours-thinks-that-only-a-small-proportion-of-people-should-earn-to-give-long-term/

But the important questions remain.

• How important is replaceability?
• Does working in banking or investment do more harm than good?

-- Even if you're donating an unusually high amount to an unusually effective charity?

• Should we be trying to change the system instead of working within it?

This should prove a good starting off point for discussion.