I don't find Eliezer's argument convincing. The infinite universe argument can be used as an excuse to do pretty much anything. Why not just torture and kill everyone and everything in our Hubble volume? Surely identical copies exist elsewhere. If there are infinite copies of everyone and everything, then there's no harm done.

That doesn't fly. Whatever happens outside of our Hubble volume has no consequence for us, and neither adds to nor alleviates our responsibility. Infinite universe or not, we are still responsible not just for what is, but also for what could be, in the space under our influence.