If everyone subscribes to this method of giving to charities, how will you get a diversity of causes that people care about/want to donate to. Some problems in this world are more complex to solve then others, hence may not do well on the effective altruism metric. As much as it's important that the giving is effective, it's also important that people feel connected to the cause (more than just a financial cheque). I'm not advocating donating time/money into mismanaged charities, but it's perfectly fine for people to contribute to slightly or somewhat less 'effective' charities if the cause is meaningful to them. If someone had a close person in their life that died from a rare disease, it's natural that people would feel an inclination to contribute to find a cure for that disease even if it may be difficult or an ineffective use of time/resources to do so ( it may also be a safety net for them especially if the disease is a genetic thing). Similarly, I spend my time researching policy as well as developing and facilitating domestic/family violence/gender and sexuality workshops, even though I don't know whether it's neccessarily effective because of it amount of gender socialisation required to solve those problems. But it's a cause extremely important to me having gone through domestic violence and abuse as well as seeing the pain in my parents' lives. This way you get a diverse range in causes, as people care and feel connected to different things. My lecturer never really answered my question on why it was unreasonable for someone who had a parent that died from a certain type of cancer to donate to that cause instead of to children in Africa.
To clarify, I definitely don't agree with everything EA has come out with (e.g. still personally nutting out Singer's challenging views on disabilities), and it has downfalls.
Personal meaning matters a lot; definitely believe that a less "effective" cause can be better to donate to or work for if it's really meaningful to you. People often donate to causes relevant to them, when they wouldn't donate to other causes, which is better than nothing. I feel, though, that we have an overwhelming tendency to focus what's right in front of our eyes, what's near to us, and are then blind to everything else. This can be a form of selfishness; effective altruism simply questions this and encourages you to look further, which doesn't mean you "have" to do everything "for the greater good" rather than what you care about.
e.g. you know the Bourke St murders earlier this year? Though it was awful, the hugeness of the outcry and portraying it as the most important thing in the world bothered me; there are many tragedies on a far greater scale that no one gives a damn about.
re. diversity of causes: EA relies on the fact that most people will ignore it, and therefore work on other non-EA-promoted causes. They've said that if everyone decided just to donate to their charities, those charities would no longer be the most effective, because they'd be oversaturated, and they would then take a different approach.
Effective altruism requires you to objectively measure and compare people's suffering such that a children in Africa are suffering more than a homeless person or someone with mental illness in Australia. Even if you can compare suffering and the above is true, it's perfectly reasonable for a person to still help a homeless person if they feel closer and more connected to the cause.
I agree that objective comparison of suffering isn't possible, and I do think EA often misses thinking about quality of life (though it does attempt to measure QALYs, quality-adjusted life years), instead simply trying to increase years of life or meet other numbers. I guess, though, we always make this subconscious judgment about what is most important, and EA just opens our eyes to making the decision more conscious and based on reason.
I see the main aim of EA as greater awareness and thoughtfulness about the impact of our actions, not dogma.