Without God there is no objective morality.
In one sentence, this summarizes the "Moral Argument" for the existence of God. Along with other classic arguments -- the ontological, teleological, cosmological and experiential -- this seeks to present a philosophical argument that proves the necessity of God. And like the other classic arguments, this one has been highly critiqued. Michael Shermer's following comments are typical of these critiques:
The argument that we cannot be good without God is easily refuted through a simple and straightforward question: What would you do if there were no God? ... Would you commit deception, robbery, rape, and murder, or would you continue being a good and moral person? ... If the answer is that people would continue being good and moral, then apparently you can be good without God.
The moral argument does not require a belief of any kind because it is based on the essential recognition that objective moral standards -- absolute right and wrong -- exist. And we know absolute right from wrong internally; they are not "given" in any documents or beliefs. We do not need the 10 Commandments to know that murder is wrong, but the 10 Commandments, instead, reinforce the moral imperatives that we already intuitively know to be true. Objective morality, then, does not rely on, or require, any external imposed belief structure, just as one does not need to "believe" in anything in order to experience the existence and qualities of love.
But where does objective morality come from? According to the moral argument it cannot arise from natural processes alone, because while random, undirected events that proceed without deliberate plan or purpose can perhaps account for the instinct of survival and procreation, they cannot account for the existence of absolute right and wrong. A universe that is random and uncreated and that operates purely on unintentional interactions can only result in subjective inclinations, not absolute morals. Friedrich Nietzsche, who asserted a universe without God, recognized this when he proposed that the driving force in human beings is the will to power, and that conventional morality is simply a restraint devised by the weak to control the powerful. Such a position can lead to horrors -- as we've seen -- but at least it is internally consistent.
The existence of objective morality necessitates a supernatural source. This is not a denial of the physical mechanism of evolution -- which is a scientific truth -- but is the assertion that the best explanation for the existence of objective morality is that it is consciously built in to the process of creation itself. And the source of this morality is the creative, conscious, sustaining power of the universe that is called God. Emmanuel Kant proposed that we are all "bound" to these moral laws, regardless of our own particular goals.
As our individual consciousness evolves, the strength of the connection to this universal consciousness, which contains moral laws, grows. The more evolved we become as a species, then, the more we connect to the morality that is embedded in creation, and the more moral we naturally become. One does not need to believe in God for this mechanism to work, as one does not need to believe in gravity for a dropped object to hit the floor.
This is the basis of moral argument, and from this perspective Shermer's questions are irrelevant because he confused cause and effect. But there still remain reasonable objections. First, there are schools of philosophy that deny the premise of the existence of objective morality, proposing that all morals are culturally derived, and that what is good for one is evil for another. This position posits that if the Nazis had won World War II then genocide and racial hatred would be seen as good, and compassion for the weak and acceptance of diversity would be seen as bad. The only reasonable response to such a position is to say that, unless one is sociopathic, we can all agree that the mass slaughter of innocents, gratuitous torture and totalitarian subjugation are absolutely morally wrong, and that freedom and compassion are absolutely good. To deny this is to embrace narcissism and nihilism.
Another objection is, "If morality is absolute, why do we see so much evil in the world?" Of course by labeling certain actions as "evil" the very question itself implies the existence of objective moral standards. If there is no morality, how can anything be called evil? Beyond this, though, the simple answer is free will. While absolute morality exists, we are free at any moment to ignore it. The continued choice to ignore the call of morality, though, damages the individual and drives him further away from humanity and true happiness.
The final objection to the moral argument is that natural processes could in fact have been responsible for absolute morality. The need to care for the group is a survival mechanism, so moral qualities such as charity and caring for the weak have arisen through natural selection. Even an act of self-sacrifice that seems to violate the instinct for survival is actually another instinct to maintain the community. While this is most likely true in many instances, there remains an internal sense that morality is more than this. Unlike an instinct that propels us, usually unconsciously, toward an act, we search deep within ourselves to find morality, and discover it in an internal "dialogue" in which we weigh options for the right answer.
If we are sensitive to this process we feel the answer coming from a higher source that aligns with the highest vision of ourselves. I have heard this alignment described as a "truth cord" that reverberates when struck with the "pitch" of the universal moral laws. Our hearts are stirred by acts of bravery and sacrifice, and are called to redress selfishness and cruelty, even at personal sacrifice. And when we strive to live in accordance with this process we are elevated and become a blessing to the world.
The moral argument is an existential recognition that there is something in us -- what some call the soul -- that insists on right action, and that these right actions are for the benefit of all living things and for the care of the Earth. This insistence that our lives be of service and contribution is a universal call that we recognize as true because we are connected to the Source of truth. This is what religions mean by the word "Holy."