Mention the philosopher and bioethics professor Peter Singer, and people tend to polarize into two groups: those who admire him for his position on animal rights, and those who despise him for his position on the rights of infants and the disabled. Reading Singer’s book The Ethics of What We Eat: Why Our Food Choices Matter (coauthored with Jim Mason) made me change to a vegetarian diet, which led to some arguments with friends who wanted to eat ethically but also ate meat. Our discussions, like Singer’s thinking, moved on to the larger question of humanity’s purpose on earth. What are our rights and responsibilities?