Interesting to meet an effective altruist here. I was somewhat involved in EA for a while and even interned at an EA org, but after reading up a bunch of different philosophies the one which I found most consistent with reality was -- perhaps surprisingly -- Objectivism.

The inferential gap between EA and Objectivism is obviously huge, so it's not worth giving a full argument here. For the intellectually curious, though, I'll simply say that the two schools of thought fromthemorning cites both assume that the purpose of morality is to maximise the greater good (rather than, say, teaching individuals principles to maximise their own long-term personal happiness).

On the off chance that someone on the fringes of the EA movement reads this, someone who shares the concerns I once had - the ultimate issue with EA is that it's hyper-empiricist: EAs love evidence but are highly distrustful of theoretical arguments. This is an understandable position, but ultimately a mistake, because you end up unable to synthesise the vast amounts of data you gather. All truths are simplifications - what you need are rules to form correct simplifications.

Objectivism isn't taken seriously in mainstream intellectual circles but it should be, because it shows how to avoid the pitfalls of both empiricism and rationalism. (See Introduction to Objectivist Epistemology for details).