Furthermore, the total number of happy humans is mostly insensitive to anything you can do, or anything happening locally within this universe, since this universe is only a tiny fraction of the overall multiverse.
Not sure about this. Even if I think I am only acting locally, my actions and decisions could have an effect on the larger multiverse. When I do something to increase happy humans in my own local universe, I am potentially deciding / acting for everyone in my multiverse neighborhood who is similar enough to me to make similar decisions for similar reasons.
I agree that this is the main way that this argument could fail. Still, I think the multiverse is too large and the correlation not strong enough across very different versions of the Earth for this objection to substantially change the bottom line.
Not sure about this. Even if I think I am only acting locally, my actions and decisions could have an effect on the larger multiverse. When I do something to increase happy humans in my own local universe, I am potentially deciding / acting for everyone in my multiverse neighborhood who is similar enough to me to make similar decisions for similar reasons.
I agree that this is the main way that this argument could fail. Still, I think the multiverse is too large and the correlation not strong enough across very different versions of the Earth for this objection to substantially change the bottom line.