I'm not the person who downvoted you, but I suspect the reason was that when you said this:

You can travel from here to China and back. Therefore, caring about China has at least a potential instrumental consequence on the rest of my life. You can't travel from here to the aliens' simulation and back, so caring about what happens there imposes costs on the rest of my life but no benefits. .... Now, if the black spheres had decent I/O capabilities and you could outsource human intellectual labor tasks to the simulations, I suppose it would make sense to care about what happens there. People can't do useful work while they're being tortured, so that wasn't the scenario in the story.

You implied that it's wrong or nonsensical to care about other people's happiness/absence of suffering as a terminal value. We are "allowed" to have whatever terminal values we want, except perhaps contradictory ones.