I know many religious people hate Sam Harris and Richard Dawkins, and perhaps some of their opinions are over the top. Nevertheless, this talk on morality and science covers some difficult and fascinating problems that are relevant for any secular theory of ethics.
There is no doubt we have certain innate moral feelings, ideas and propensities: these are the result of evolution by natural selection. But trying to justify an ethical system by simply appealing to this nature is unsound. It commits the appeal to nature fallacy. One needs a rational justification for ethical ends and how to behave to achieve these ends.
I like the comments of Harris on how standard consequentialism needs to be revised and how notions of justice and fairness are not incompatible with a consequentialist theory of ethics.