Ben Kuhn, playing Devil's advocate:
Effective altruists often express surprise that the idea of effective altruism only came about so recently. For instance, my student group recently hosted Elie Hassenfeld for a talk in which he made remarks to that effect, and I’ve heard other people working for EA organizations express the same sentiment. But no one seems to be actually worried about this—just smug that they’ve figured out something that no one else had.
The “market” for ideas is at least somewhat efficient: most simple, obvious and correct things get thought of fairly quickly after it’s possible to think them. If a meme as simple as effective altruism hasn’t taken root yet, we should at least try to understand why before throwing our weight behind it. The absence of such attempts—in other words, the fact that non-obviousness doesn’t make effective altruists worried that they’re missing something—is a strong indicator against the “effective altruists are actually trying” hypothesis.
I think this is a good point. If you find yourself in a small group advocating for an obvious and timeless idea, and it's 2014, something a bit strange is probably going on. As a side note, if people actually come out and disagree, this is more worrying and you should really take some time out to be puzzled by it.
I can think of a few reasons that 'effective altruism' might seem so obvious and yet the EA movement might only just be starting.
I will assume that the term 'effective altruism' is intended to mean roughly what the words in it suggest: helping other people in efficient ways. If you took 'effective altruism' to be defined by principles regarding counterfactual reasons and supererogatory acts and so on, I don't think you should be surprised that it is a new movement. However I don't think that's what 'effective altruism' generally means to people; rather these recent principles are an upshot of people's efforts to be altruistic in an effective manner.
Explanation 1: Turning something into a social movement is a higher bar than thinking of it
Perhaps people have thought of effective altruism before, and they just didn't make much noise about it. Perhaps even because it was obviously correct. There is no temptation to start a 'safe childcare' movement because people generally come up with that on their own (whether or not they actually carry it out). On the other hand, if an idea is too obviously correct for anyone to advocate for, you might expect more people to actually be doing it, or trying to do it. I'm not sure how many people were trying to be effective altruists in the past on their own, but I don't think it was a large fraction.
However there might be some other reason that people would think of the idea, but fail to spread it.
Explanation 2: There are lots of obvious things, and it takes some insight to pick the important ones to emphasize
Consider an analogy to my life. Suppose that after having been a human for many years I decide to exercise regularly and go to sleep at the same time every night. In some sense, these things are obvious, perhaps because my housemates and parents and the media have pointed them out to me on a regular basis basically since I could walk and sleep for whole nights at a time. So perhaps I should not be surprised if these make my life hugely better. However my acquaintences have also pointed out so many other 'obvious' things - that I should avoid salt and learn the piano and be nice and eat vitamin tablets and wear make up and so on - that it's hard to pick out the really high priority things from the rest, and each one takes scarce effort to implement and try out.
Perhaps, similarly, while 'effectiveness' and 'altruism' are obvious, so are 'tenacity' and 'wealth' and 'sustainability' and so on. This would explain the world taking a very long time to get to them. However it would also suggest that we haven't necessarily picked the right obvious things to emphasize.
If this were the explanation, I would expect everyone to basically be on board with the idea, just not to emphasize it as a central principle in their life. I'm not sure to what extent this is true.
Explanation 3: Effectiveness and altruism don't appear to be the contentious points
Empirically, I think this is why 'effective altruism' didn't stand out to me as an important concept prior to meeting the Effective Altruists.
As a teen, I was interested in giving all of my money to the most cost-effective charities (or rather, saving it to give later). It was also clear that virtually everyone else disagreed with me on this, which seemed a bit perplexing given their purported high valuation of human lives and the purported low cost of saving them. So I did actually think about our disagreement quite a bit. It did not occur to me to advocate for 'effectiveness' or 'altruism' or both of them in concert, I think because these did not stand out as the ideas that people were disagreeing over. My family was interested in altruism some of the time, and seemed reasonably effective in their efforts. As far as I could tell, where we differed in opinion was in something like whether people in foreign countries really existed in the same sense as people you can see do; whether it was 'okay' in some sense to buy a socially sanctioned amount of stuff, regardless of the opportunity costs; or whether one should have inconsistent beliefs.
Explanation 4: The disagreement isn't about effectiveness or altruism
A salient next hypothesis then is that the contentious claim made by Effective Altruism is in fact not about effectiveness or altruism, and is less obvious.
'Effective' and 'altruism' together sound almost tautologically good. Altruism is good for the world almost by definition, and if you are going to be altruistic, you would be a fool to be ineffective at it.
In practice, Effective Altruism advocates for measurement and comparison. If measurement and comparison were free, this would obviously be a good idea. However since they are not, effective altruism stands for putting more scarce resources into measurement and comparison, when measurement is hard, comparison is demoralizing and politically fraught, and there are many other plausible ways that in practice philanthropy could be improved. For instance, perhaps it's more effective to get more donors to talk to each other, or to improve the effectiveness of foundation staff at menial tasks. We don't know, because at this meta level we haven't actually measured whether measuring things is the most effective thing to do. It seems very plausible, but this is a much easier thing to imagine a person reasonably disagreeing with.
Effective altruists sometimes criticize people who look to overhead ratios and other simple metrics of performance, because of course these are not the important thing. We should care about results. If there is a charity that gets better results, but has a worse overhead ratio, we should still choose it! Who knew? As far as I can tell, this misses the point. Indeed, overhead ratio is not the same as quality. But surely nobody was suggesting that it was. If you were perfectly informed about outcomes, indeed you should ignore overhead ratios. If you are ignorant about everything, overhead ratios are a gazillion times cheaper to get hold of than data on results. According to this open letter, overhead ratios are 'inaccurate and imprecise' because 75-85% of organizations incorrectly report their spending on grants. However this means that 15-25% report it correctly, which in my experience is a lot more than even try to report their impact, let alone do it correctly. Again, the question of whether to use heuristics like this seems like an empirical one of relative costs and accuracies, where it is not at all obvious that we are correct.
Then there appear to be real disagreements about ethics and values. Other people think of themselves as having different values to Effective Altruists, not as merely liking their aggregative consequentialism to be ineffective. They care more about the people around them than those far away, or they care more about some kinds of problems than others, and they care about how things are done, not just the outcome. Given the large number of ethical disagreements in the world, and unpopularity of utilitarianism, it is hardly a new surprise that others don't find this aspect of Effective Altruism obviously good.
If Effective Altruism really stands for pursuing unusual values, and furthermore doing this via zealous emphasis on accurate metrics, I'm not especially surprised that it wasn't thought of years ago, nor that people disagree. If this is true though, I fear that we are using impolite debate tactics.