Michael Martin makes a few good points regarding the claim that without religion there is no basis for morality:
Is Theistic Morality Necessarily Objectivist?:
Let us assume for the moment that the Biblical position on rape is clear: God condemns rape. But why? One possibility is that He condemns rape because it is wrong. Why is it wrong? It might be supposed that God has various reasons for thinking rape is wrong: it violates the victim’s rights, it traumatizes the victim, it undermines the fabric of society, and so on. All of these are bad making properties. However, if these reasons provide objective grounds for God thinking that rape is wrong, then they provide objective grounds for others as well. Moreover, these reasons would hold even if God did not exist. For example, rape would still traumatize the victim and rape would still undermine the fabric of society even. Thus, on this assumption, In this case, atheists could provide objective ground for condemning rape–the same grounds used by God.
Let us suppose now that rape is wrong because God condemns it. In this case, God has no reasons for His condemnations. His condemnation makes rape wrong and it would not be wrong if God did not condemned it. Indeed, not raping someone would be wrong if God condemned not raping. However, this hardly provides objective grounds for condemning rape: Whether rape is right or wrong would be based on God’s arbitrary condemnation. On this interpretation, if atheists can provide no objective grounds for condemning rape, they are no worse off than theists. However, as we have seen, there is no reason to suppose that they cannot provide such grounds.
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