Advocates of religion often argue that religion is necessary to provide an objective grounding for morality. The obvious problem with this argument is that only something non-fictional can provide objective grounding for something else. Therefore religion fails to provide objective grounding for anything because religion is fiction. In other words, the horse pulls the cart, the cart does not pull the horse. So even if religion would provide an objective basis for morality if religion were true, the religion horse is fiction so it is incapable of pulling any cart of objectivity. People can pretend that religion is true and from there they can pretend that morality has objective grounding in their religion, but pretending objectivity is self-contradictory, it is disengenuity.
Having dismissed religion, the question of objectivity remains. Contrary to what some advocates of religion claim, objectivity is clearly not dependent on religion. We are objectively better off seeking the assistance of medical doctors who are trained and licensed according to the principle of following the empirical evidence than we are going to religious faith healers with magic potions and dances and traditional rituals. What about morality? Is there an objective basis for morality?
Some atheists, such as Jerry Coyne, assert there is no objective morality. Other atheists, such as philosopher Dan Fincke (and neuroscientist Sam Harris), argue that morality is empirically rooted in human flourishing and therefore, in the main, objective. I have read both sides of this argument and there is a winner: Dan Fincke is correct. Take a look at Dan Fincke disputing Jerry Coyne on his blog Empowerment Ethics: “Can There Be Objective Morality When So Many People Disagree About Morality?” Human flourishing would arguably be enhanced if everyone who has more than the bare minimum that they need gave away everything non-essential that they owned to those who otherwise lack what they need to survive. Jerry Coyne has a fair point that almost no one does that or advocates that everyone do that. But this lack of perfection in practice, as with the lack of perfect and complete empirical knowledge or the lack of universal agreement, does not defeat the successful argument that there is an objective basis for evaluating morality.
Some people may object to the self-indulgence of the human flourishing criteria. This concept does generalize so that, for example, we can evaluate morality of other animals by their behaviors to each other and also of cross-species behaviors. But any practical morality must prioritize, and humans are the proper priority of us humans.