The current issue of the Oxford Left Review has a debate between socialist Pete Mills and two 80,000 hours people, Ben Todd and Sebastian Farquhar: The Ethical Careers Debate, p4-9. I'm interested in it because I want to understand why people object to the ideas of 80,000 hours. A paraphrasing:
- Todd and Farquhar
- Choose your career to most improve the world. Focus on the consequences of your decisions.
- 80,000 hours says you must work a high paying but world-destroying career so you can give more money away. Then "your interests are aligned with the interests of capital" and you can't use political means to improve the world because that endangers your career.
- Todd and Farquhar
- Professional philanthropy is one option, but so are research and advocacy. Even if you go the high paying career route, you could be a doctor. Even if you take a people-harming but well paying job you're just replacing someone else who would do it instead. Engels was a professional philanthropist, funding Marx's reasearch.
- "80k makes much of replaceability: 'the job will exist whatever you do.' This is stronger than the claim that someone else will become a banker; rather, it states that there will always be bankers, that there will always be exploitation." Engles took on too much by trying to be both a professional philanthropist and an activist which drove him to depression and illness.
- Todd and Farquhar
- Campaigning might be better than professional philanthropy, though you should consider whether you do better to get a well-paying job and fund multiple people to campaign. Replaceability means that a given job will exist whether you take it or not, but "there might be some things you could do that would cause the job to cease to exist; for instance, by campaigning against banking". "Even if you believe capitalism is one of the world's greatest problems, you shouldn't make the seductive inference that you should devote your energies to fighting it. Rather, you should work on the cause that enables you to make the biggest difference. There may be other very big problems which are more tractable."
- "The language of probability will always fail to capture the possibility of system change. What was the expected value of the civil rights movement, or the campaign for universal suffrage, or anticolonial struggles for independence? As we have seen most recently with the Arab Spring, every revolution is impossible, until it is inevitable." I don't like that 80,000 hours uses calculations in their attempt to estimate the good you could do through various potential careers. Stop focusing on the individual when the system is the problem. [Other stuff that doesn't make sense to me.]
As a socialist, Mills really doesn't like the argument that the best way to help the world's poor is probably to work in heavily capitalist industries. He seems to be avoiding engaging with Todd and Farquhar's arguments, especially replaceability. He also really doesn't like looking at things in terms of numbers, I think because numbers suggest certainty. When I calculate that in 50 years of giving away $40K a year you save 1000 lives at $2K each, that's not saying the number is exactly 1000. It's saying 1000 is my best guess, and unless I can come up with a better guess it's the estimate I should use when choosing between this career path and other ones. He also doesn't seem to understand prediction and probability: "every revolution is impossible, until it is inevitable" may be how it feels for those living under an oppressive regime but it's not our best probability estimate. 
In a previous discussion a friend also was mislead calculations. When I said "one can avert infant deaths for about $500 each" their response was "What do they do with the 500 dollars? That doesn't seem to make sense. Do they give the infant a $500 anti-death pill? How do you know it really takes a constant stream of $500 for each infant?". Have other people run into this? Bad calculations also tend to be distributed widely, with people saying things like "one pint of blood can save up to three lives" when the expected marginal lives saved is actually tiny. Maybe we should focus less on estimates of effectiveness in smart-giving advocacy? Is there a way to show the huge difference in effect between the best charities and most charities without using these?
Maybe I should have way more of these discussions, enough that I can collect statistics on what arguments and examples work and which don't.
(I also posted this on my blog)
 Which is not to say you can't have big jumps in probability estimates. I could put the chance of revolution at 5% somewhere based on historical data but then hear some new information about how one has just started and sounds really promising which bumps my estimate up to 70%. But expected value calculations for jobs can work with numbers like these, it's just "impossible" and "inevitable" that break estimates.