There's no temporal infinity without spatial infinity (instead you typically get eternal return). There's incredibly weak evidence for spatial infinity - since we can only see the nearest 13 billion light years - and that's practiacally nothing - compared to infinity.

The situation is that we don't know with much certainty whether the world is finite or infinite. However, if an ethical system suggests people behave very differently here and now depending on the outcome of such abstract metaphysicis, I think that ethical system is probably screwed.