I take you to mean "what would maximize Luke's utility function" (knowing that 'utility function' is probably just a metaphor when talking about humans) when you say "you actually should..." Of course, my 'utility function' is unknown to both of us.

In that case, it would remain true in our hypothetical scenario that I should-HumanLivesAreGood donate to VillageReach (assuming they're a good charity for saving human lives), while I should-UtilityFunctionLuke donate to SaveTheMosquitos.

(Sorry about formatting; LW comments don't know how to use underscores, apparently.)