Are there not philosophers who defend objective morality, non-theistically? Well, the old 'uns were mostly theists, anyway, e.g. Plato.
Hi Wiggs,
Sam Harris, noted American atheist, is an exponent of moral realism. He suggests the following, for instance.
"For there to be objective moral truths worth knowing, there need only be better and worse ways to seek happiness in this world. If there are psychological laws that govern human well-being, knowledge of these laws would provide an enduring basis for an objective morality.... Everything about human experience suggests that love is more conducive to human happiness than hate is."
Sam Harris, "Letter to a Christian Nation", p23.
Of course he strongly rejects the idea that belief in an objective morality depends on believing in a god and he also accepts that we do not have anything like a final scientific understanding of human morality. In fact, he does seem to me to be talking about human flourishing here, which I do not disagree with. However I would challenge the idea that this in some way suggests an objective morality.
I accept that there is a 'potential' for morality, if it aids survival. However I see this as no different to any other 'potentials' such as the eye, movement, ability to breed, speed, strength, selfishness and a myriad of other characteristics of living things. I do not see these 'potentials' as having any outside existence in their own right, and, therefore do not regard them as objective in the sense of having an existence separate from the creatures which exhibit these characteristics.
I rather go along with these words of E. O. Wilson:
"Either ethical principles, such as justice and human rights, are independent of human experience, or they are human inventions. The distinction is more than an exercise for academic philosophers. The choice between these two understandings makes all the difference in the way we view ourselves as a species. It measures the authority of religion, and it determines the conduct of moral reasoning."
http://www.theatlantic.com/magazine/archive/1998/04/the-biological-basis-of-morality/377087/