Given the choice you just described our Universe vs. all other universes, I'd fight for ours I think. You may say genocide of all future people is an unimaginable atrocity, but then again, not stopping the unimaginable genocide of every currently concious being is also a genocide of enourmous porportions. The difference is, one way I'm capable of thought. The other I'm not. But it's not just me, it's everyone I know and love, everything I know and love, every fiber of every being I've ever interacted with. Now, you can call this selfish, but honestly, I'm not sure I care about the fututre "lives" (as life is no guarentee in a universe) of beings I've never met, who are nothing like me, who have no connection to me and who are inherently incomprihensible to me. I don't see it as all currently existing life vs. all future life. I see it as all currently existing life vs. the potential for life in a form we don't automatically understand or reconize. The beings in the this universe might be literally incapable of thought. Or they might not exist at all. It's kinda like the evil we know vs. the evil we don't.... only replace evil with life.

Plus, as a hero in this spot, imagine that your calculations were WRONG. I'm not arrogant enough to think that even as a god-being, I couldn't have made a mistake. Somewhere in the unfathomably difficult experiments and incompriehnsible calculations you forgot a decimal point. And that decimal point meas that there is no subsequent big bang. There's just us and not us. A single mis-calculation and you're weighing the lives of everything concious now against the infinite unending void. Failure to act means that void consumes all life. Forever.