Can man be moral without God? What about atheists who claim one doesn’t need religion to be moral? Does every bit of morality we have stem from the Bible? What about cultural differences?
Please forgive the slow response. I believe that it is possible to be moral without being a Christian, however it is, arguably, not possible to be moral if one is an atheist. This is a debatable point. The debate probably hangs as much on the question of definition of words as it does on anything else, so it is possible to get into an unhelpful debate on this, so I suggest you define your terms carefully with friends when discussing this question. Let me explain.
First of all, l need to provide a solid definition of moral behavior, then I need to defend my statement that a non-Christian can behave morally, and then my claim that an atheist cannot.
The definition that I will use is this: Moral behavior is a life lived according to a received definition of what is morally “right” and morally “wrong” to do. My definition of morality only makes sense if there is an absolute moral definition of what is right and wrong behavior. This is the normal definition of morality. Morality has to do with absolute right and absolute wrong. For example, according to Christian morality, it is immoral to take a life for selfish purposes. It is immoral to steal the property of another. Purposefully deceiving in order to achieve personal gain is also immoral. It is immoral to have sex with someone with whom one is not married. These are absolute moral truths, not simply a personal opinion. There is also moral “good” in Christianity. It is morally good to help a person in need, to make peace between warring people, to shine the light of truth in places where evil is prevalent and to love both those who love us and those who do not.
Can a Hindu or Buddhist or Jain or Muslim behave morally? I would say that by the definition I have given above, the answer is a provisional yes. We can debate whether Muslim or Hindu ideas of moral truth are absolute and are received from a morally certain source of such morality. However, surely to the practitioner of such a religion, this moral truth is accepted as absolute and this person can be thought of as behaving in a moral way. Therefore, I am not so sure that I would agree that “every bit of morality we have comes from the Bible.” I am sure some will debate this, but I believe that we can find common ground with the members of other religions on moral grounds and we ought to use this common ground as a means to proceed to other discussions.
Then there is the question of whether an atheist or agnostic can be moral. The atheist worldview denies the existence of absolute moral truth. Arguably, the agnostic would agree that there is no absolute good and evil, and therefore morality is at best undefinable. In fact, one of the strongest arguments for the existence of God is known as the Moral Argument. It goes something like this:
Premise: Absolute moral truth exists.
Argument: Such absolute moral truth can exist only if there is an authoritative source of such absolute truth.
Conclusion: If the premise is correct, then God must exist, as the only conceivable source of such moral truth is a supernatural source of such truth.
Now, the atheist will tend to resist this argument (both the moral argument for God and the argument that they are not able to behave morally). Actually, some of the most honest and consistent atheists will agree with the premise that morality is meaningless in an atheist worldview. However, most atheists resist this idea, as it makes their worldview appear to be flawed or even dangerous to the human good. Authors such as Richard Dawkins try to redefine the word morality in such a way that there is such a thing as atheist morality. He argues that morality is the result of certain Darwinian processes. I believe that such spin is ineffective. What they do is turn personal ethics into a false kind of pseudo-morality which robs the word of real meaning. Moral truth which is not absolute is not moral truth and Dawkins’ morality is certainly not absolute.
In conclusion, you may not win an atheist friend over to the premise that it is not possible to be moral without God, but on a logical basis, it is perfectly logical and reasonable to state that without religion there is no morality.
As for cultural differences, a moral truth is a moral truth. If it is immoral to steal or to lie or to kill or to have sex with a person one is not married to, then cultures cannot change this. Ethics can be culture-specific, but morality cannot. It is possible to be stuck with a choice between two evils. For example, one might justify lying to a terrorist to avoid the death of another, but this would not be an example of culture affecting morality. The normal definition of morality as I understand it is unaffected by culture.