Keep in mind that this "rationality" is just a word. Making up a word shouldn't, on its own, be enough to show that something is good or bad. If self-interest is more "rational" than helping others, then you should be able to give good reasons for that with other words that are more clear and simple.
People get very confused when they start thinking that what they actually want matters less than some piece of paper saying what they Should or Shouldn't want. Even if some made-up idea says you Shouldn't want to help others except to make yourself happy, why should that matter more to me than what I actually want, which is just to help people? This is a lot like Mr. Yudkowsky's "being sad about having to think and decide well".
Btw, that link is really good and it made me think a bit differently. I've sometimes envied others for their choices and thought I'm supposed to behave in a certain way that is opposite to that... but actually what matters is what I want and how I can achieve my desires, not how I'm supposed to act.
xkcd's Up-Goer Five comic gave technical specifications for the Saturn V rocket using only the 1,000 most common words in the English language.
This seemed to me and Briénne to be a really fun exercise, both for tabooing one's words and for communicating difficult concepts to laypeople. So why not make a game out of it? Pick any tough, important, or interesting argument or idea, and use this text editor to try to describe what you have in mind with extremely common words only.
This is challenging, so if you almost succeed and want to share your results, you can mark words where you had to cheat in *italics*. Bonus points if your explanation is actually useful for gaining a deeper understanding of the idea, or for teaching it, in the spirit of Gödel's Second Incompleteness Theorem Explained in Words of One Syllable.
As an example, here's my attempt to capture the five theses using only top-thousand words:
If you make a really strong computer and it is not very nice, you will not go to space today.
Other ideas to start with: agent, akrasia, Bayes' theorem, Bayesianism, CFAR, cognitive bias, consequentialism, deontology, effective altruism, Everett-style ('Many Worlds') interpretations of quantum mechanics, entropy, evolution, the Great Reductionist Thesis, halting problem, humanism, law of nature, LessWrong, logic, mathematics, the measurement problem, MIRI, Newcomb's problem, Newton's laws of motion, optimization, Pascal's wager, philosophy, preference, proof, rationality, religion, science, Shannon information, signaling, the simulation argument, singularity, sociopathy, the supernatural, superposition, time, timeless decision theory, transfinite numbers, Turing machine, utilitarianism, validity and soundness, virtue ethics, VNM-utility