Nature gives mixed messages about morality. A morality based in nature is vulnerable to large-scale abuse. From a Christian perspective, the new science of evolutionary psychology founders on its anthropology, the nature of the human condition. You are a cosmic accident. You are no different from other animals.
All morality is arbitrary.
You must look down, not up, in order to understand yourself. They call on us to respect the rights of animals without giving us a rationale for these rights. In a word their system is contradictory and severely problematic. They need the discipline and informed power of God's revelation to bring consistency and sense to their absurd system of contentions.