"Just as there is no such thing as Christian physics or Muslim Algebra, we will see that there is no such thing as Christian or Muslim morality."[1]
Setting the Canvas
Morality is a human construct. The idea was devised and revised by human beings. The ideas like altruism that we associate with morality have a very natural explanation. They are merely survival adaptations that have allowed our species and many others to function in cooperative societal groups. We see these traits in countless other species, and time after time we see just how they benefit the species and social groups tremendously.
But we also see the ugly or bad traits present as well. One of the best examples of these immoral or bad traits we see comes in the form of social unrest that leads to violence. You see, even we social animals still carry the instincts that have kept our species alive for so long. Instincts like territorialism are strong in many social animals, especially primates like us and all our cousins. These instincts lead to what we humans call emotions such as jealousy and hatred. While we think of those things as being immoral, and we know how detrimental they can be, we cannot think of them as unnatural. They are, like altruism, an inherent part of what we have evolved from and what we are evolving into.
Keeping this in mind, one can see that as we humans look to paint the moral landscape we see before us, it is like trying to capture a moving image on canvas. But all too often, people have claimed to paint this landscape perfectly, only for us to come along later and see that the painting does not resemble the landscape before us at all. So this begs the question, "Can we paint this landscape at all?"
Wetting the Brush
As I said before, morality is a human construct. Now what I mean by this is that it is an idea designed by humans that only applies to humans. Unlike the laws of physics and such, morality has no implications for any other animals in the known universe. We would certainly not deem a lion immoral for killing a weak cub, although we may think it cruel. Only the lion and it's social group can determine what is moral for them. We can not tell the lion how to be moral, because we are not a part of the lion's society and have no right to tell the lion how to behave.
Similarly, our ideas of morality can not come from outside of our social groups. This is why we see moral relativism as the prevailing idea in our world. What is deemed good for one society may be deemed immoral for another. This perspective does not sit well with the theist, regardless of how patently obvious it is. You see, the theist believes that morality is the construct of an outside agent usually referred to as god. According to them, back when gods talked to men, their gods have given mankind moral codes and those are the codes we're all supposed to live by.
Of course, the obvious problem with that logic is that the paintings they're selling don't look anything like the landscape we see before us. It's as if we asked to see an ocean sunset and were instead handed a painting of a barren wasteland. It simply isn't what we asked for and many of us refuse to pay for something we didn't ask for and honestly don't see any value in.
Laying the Base Coat
I won't be dishonest and act as if religion has offered no contributions to this painting of the moral landscape. Indeed, many religions have contributed greatly to our perception of how we might live in a more civilized and peaceful society. But the ideas started long before these religions and the one big problem with most of these religions is stagnation. They made headway to get certain concepts clear, like that one ought not murder another person, but they stopped progressing even as human knowledge and understanding pressed forward.
We atheists call these doctrines archaic and barbaric, not simply as an insult, but to highlight how they compare to the landscape before us. We evaluate them and the ideas they present by the knowledge and understanding we have now. When we see ideas such as sexism, slavery, and homophobia being presented as noble, we call those ideas to task because we've seen them to be both false and detrimental. And for this we are called arrogant and hateful.
The truth is that we are merely trying our best to paint this landscape as it actually appears rather than paint the scene that we would like to see. We are trying to address injustice based on the evidence before us rather than some archaic perception of a mold everyone should fit into. In the end it is up to us to set the standards and raise the bar when new evidence presents itself, and those unwilling to meet those standards should be taken to task on their refusal to do so.
References:
[1] Sam Harris from The Moral Landscape