Some people feel ashamed when doing this kind of math with human lives. I feel ashamed when not doing it.

For most people, the goal of any altruistic act is simply to do something helpful. Very few of us choose where to donate, where to volunteer, and how to live our lives based on the answer to the question, “How can I do the most possible good in the world?” And yet it is that calculating attitude that is crucial to helping as many animals (or people) as possible.