David, we're not defining rationality to exclude other-oriented desires. We're just not including that exact morality into the word "rational". Instrumental rationality links up a utility function to a set of actions. You hand over a utility function over outcomes, epistemic rationality maps the world and then instrumental rationality hands back a set of actions whose expected score is highest. So long as it can build a well-calibrated, highly discriminative model of the world and then navigate to a compactly specified set of outcomes, we call it rational, even if the optimization target is "produce as many paperclips as possible". Adding a further constraint to the utility function that it be perfectly altruistic will greatly reduce the set of hypothetical agents we're talking about, but it doesn't change reality (obviously) nor yield any interesting changes in terms of how the agent investigates hypotheses, the fact that the agent will not fall prey to the sunk cost fallacy if it is rational, and so on. Perfectly altruistic rational agents will use mostly the same cognitive strategies as any other sort of rational agent, they'll just be optimizing for one particular thing.

Jane doesn't have any false epistemic beliefs about being special. She accurately models the world, and then accurately calculates and outputs "the strategy that leads to the highest expected number of burgers eaten by Jane" instead of "the strategy that has the highest expected fulfillment of all thinking beings' values".

Besides, everyone knows that truly rational entities only fulfill other beings' values if they can do so using friendship and ponies.