So I'm wondering why so many smart, compassionate people favor developing-world charities. They seem like a good bet if you're not aware of more-marginal causes, but they don't make a whole lot of sense to me otherwise. There are far more animals than humans, and there will be far more future humans/post-humans/animals than there are current humans. I'm wondering whether I'm missing something. Here are the explanations I came up with.
Evaluation. Some developing-world charities have been vetted, and some outstanding ones have been identified by GiveWell and GWWC. Animal charities haven't been evaluated nearly as thoroughly. Existential-risk charities seem even worse in this respect, and they're inherently hard to evaluate.
If this is the problem, it seems that people should just fund evaluation of the under-evaluated charities, since the value of information is so great. If this isn't practical right now, they could wait.
Popularity. Developing-world health is a more popular cause than animal welfare or existential risk. If many people believe something, it's probably for a reason—maybe even a good one. Better to follow the conventional wisdom now, and change our minds later when we have more information.
Popularity might be a useful heuristic, but there ultimately has to be a rationale. Otherwise, this is just circular reasoning.
Uncertainty about the future. People might resist giving to organizations such as the SIAI because of the uncertainty about its effects. It could be making things better, it could be making things worse, or it could simply be irrelevant.
But giving to developing-world health has exactly the same problem. The vast majority of the value of such giving is concentrated in the far future. Will giving to developing-world health increase or decrease existential risk? It's not clear, but this factor dominates the expected-value calculation.
Public image. It's easier to get people to give to developing-world health than to animal welfare or existential-risk reduction. So maybe we should promote what's more palatable, and focus on more-marginal causes later.
There's something to this. Maybe it's better to try to get prospective do-gooders to start giving to mainstream charities. But it still seems that we should focus our own money on whatever causes are most effective. It might be the case that my picture of which organizations like-minded people give to is distorted for this reason (i.e., people are trying to seem more mainstream)
Other (less-good) explanations. Animals aren't sentient, or if they are, they don't matter. Future generations don't matter, or we can apply a discount rate to their welfare. Third-world charities produce tangible benefits, while existential-risk and animal-welfare charities have effects that are delayed or indirect. Bill Gates and Warren Buffett fund developing-world health. Developing-world health is a "sure" bet.
Are there other (good) reasons, or did I not do justice to some of the ones I listed?