For 1, we'd have broadly different priorities in such a world and different jobs for people to fill. Chemist wouldn't be the only other option. We might prioritize infrastructure more to increase productivity, and construction workers could work on that, or in some other non-construction area.
(written by a development economist)
Helping others is good. Especially helping the ones who lost the lottery of birth.
However, I see substantial flaws in Peter Singer's narrative, Give Well and EA which haven't been addressed so far.
1. Criticism towards consumption and luxury
Peter Singer often criticized all kinds of luxurious goods. Let's assume that all humans act upon Singer's narrative. Instead of buying swimming pools for their garden, they donate the money to NGO's that distribute vaccines. Hundreds of thousands construction workers would lose their job. Unemployed people have a 30% higher suicide risk than employed ones. They cannot be reemployed as chemists for the Pharma companies that produce the vaccines. Consequently, the government has a) less tax income and b) more expenditures due to employment benefits. Therefore, the construction worker will donate less and the government may reduces its foreign aid budget. This example shows that consumption and thus a strong economy in a Western country is not only important for wealthy people in the West but also for the bottom billion. It's not an either or choice. A strong economy is the foundation for everything.
2. The drowning child metaphor does not apply in most real world scenarios
"It is an illusion that lives can be bought like cars." - Angus Deaton.
What I see from cases of starvation is that they happen because
a) NGO's are not permitted in this area
b) The affected person and their family does not reach out to an NGO, hospital etc.
Capital does not seem to be the bottleneck here.
Another example is Malaria. By stating that you can save a life for $5000, Give Well applies that if there only is enough money provided, everyone could be saved from Malaria. However, no matter how many bed nets are distributed, there will still be people dying from Malaria since they can be infected during the day. Currently, there is no effective vaccine yet. Even if there was one, it is estimated that only 80% of the people can be reached. The remaining 20% have to addressed through gene edited mosquitos. In total, there is $4.3bn invested in the fight against Malaria every year.
So, do I have certainty that $5000 save a life? No, I don't. I don't know if my $5000 saves the drowning child.
3. 80,000 hours applies a detrimental mindset
If someone's biggest passion is becoming a musician, the highest value this person can provide to society is becoming a musician. It's not expedient if she becomes a climate researcher or development worker etc is she is not the best possible person for this job and if it doesn't make her happy. As a society, you create the biggest value and happiness if everyone does what they truly want to do - no matter what it is (obviously within legal limits). In an interview at the SRF, Peter Singer even argued against professional musicians since there are more worthy jobs. If a moral committee decides what kind of jobs are allowed to exist instead of the individual, this would be a gloomy, unfree and unhappy world with a much lower GDP to distribute.
4. Hundreds of millions are invested in the research of speculative scenarios
Humans are bad to predict what's going to happen next year. Why should they be able to do a good job in predicting what happens in >100 years? 50 years ago, The Club of Rome published the book "limits to growth". They said that the world will run out of gold in 1979, silver in 1983, oil in 1990 and gas in 1992. Well, we know now that these predictions are false. Isn't it smarter to wait until there is more certainty about the future and its technologies to deepen the research?
One could also argue that these hundreds of millions should rather be invested in cash transfers to people living in extreme poverty enabling them to increase local consumption, sending their children to school and thus boosting the local economy.
5. What is the best possible option?
How can we create the happiest world possible? I believe by letting people live the life they truly want to live (yes, including luxury) and by making them donate 1% of their income. Much less than 1% of the income of the wealthiest 25% globally is enough to eradicate extreme poverty via cash transfers. The financial burden due to global inequality should be distributed equally. Like a tax. In the same time, people should be encouraged to follow their passion and fulfill their wildest dreams, no matter what they are.
I agree that any time you spend money on one thing instead of something else, you're missing the good that could have come out of one thing. But it's still better to spend money on some things than other things. There is no choice that has no downsides. And even if there were, I would prefer a choice with small downside and large upside over a choice with zero upside and zero downside.
I don't think you are correctly applying marginal thinking. GiveWell doesn't need to claim that $5000 spent sufficiently many times can prevent every death due to malaria. It only needs that $5000 can save a marginal life, which it can.