Just in case I failed to make it clear, it is not my opinion that the calculation I described means that we should all give everything beyond what we need to charity, or that we should all give everything beyond some fixed threshold, or anything of that kind. I don’t think weighted utilitarianism is necessarily a good system, nor do I think it’s clear that (e.g.) motivational effects don’t make a big enough difference to invalidate that naive calculation completely.
Just in case I failed to make it clear, it is not my opinion that the calculation I described means that we should all give everything beyond what we need to charity, or that we should all give everything beyond some fixed threshold, or anything of that kind. I don’t think weighted utilitarianism is necessarily a good system, nor do I think it’s clear that (e.g.) motivational effects don’t make a big enough difference to invalidate that naive calculation completely.