First off, regarding your hypothetical, it would be no contest. Replacing earth with a box of ice cream would have about the same decision time. You could frame it as a more active choice, akin to the trolley problem - have me convince Galactus to change course towards Earth - I wouldn't mind.

Now where you go wrong is assuming that somehow implies that I do not value the lives of my fellow human beings, or of mankind overall. On the contrary, I am quite concerned about x-risk, and I would be too if there were no family to be affected. It is just not the priority goal.

Consider you had a choice between the life of a non-human primate, xor that of a human. Just because you (hypothetically) quickly decide to save the human does not mean you do not value the non-human primate, or that without another high-priority preference involved, you would not invest a lot into saving that animal. Do you see the point?

If you believe that most of LW is irrational on this topic - saving the world - then it seems that you should be fixing that.

No, why would you think that? I do share that value, and I obviously would as a derived value even if I only did care about my family (repercussions). But even without such considerations, I'd care about it. I'd just accept no tradeoff whatsoever compromising between other humans and "my" humans. What's to defend about that? As I wrote elsewhere, it's not a "bias" in any sense of the word as it's used around here.

Lastly, again with that curious choice of calling preferences "irrational". As if we could just argue towards which preferences to rationally choose. Which ice cream flavor we really should enjoy the most.