Kind of the point.
how could we possibly act on anything but our own desires?"
Our actions are not directly determined by our desires.
I would not call an action that I do not decide to bring about "my action".
What are we disagreeing on apart from wording? One can only do what is right if one desires to do what is right. There are many barriers between that and what actually gets done (which is why FAI is a good idea). A brain with Tourettes and one without Tourettes but with the same desires are effectively the same decision making process in different environments, up to the approximation that brains are decision making processes.
In You Provably Can't Trust Yourself, Eliezer tried to figured out why his audience didn't understand his meta-ethics sequence even after they had followed him through philosophy of language and quantum physics. Meta-ethics is my specialty, and I can't figure out what Eliezer's meta-ethical position is. And at least at this point, professionals like Robin Hanson and Toby Ord couldn't figure it out, either.
Part of the problem is that because Eliezer has gotten little value from professional philosophy, he writes about morality in a highly idiosyncratic way, using terms that would require reading hundreds of posts to understand. I might understand Eliezer's meta-ethics better if he would just cough up his positions on standard meta-ethical debates like cognitivism, motivation, the sources of normativity, moral epistemology, and so on. Nick Beckstead recently told me he thinks Eliezer's meta-ethical views are similar to those of Michael Smith, but I'm not seeing it.
If you think you can help me (and others) understand Eliezer's meta-ethical theory, please leave a comment!
Update: This comment by Richard Chappell made sense of Eliezer's meta-ethics for me.