They believe that the Bible is the word of God. You believe that it isn't. The question remains however. By what authority do you claim anything to be moral or immoral?
This is actually
begging the question. You assume that making a moral claim must be backed up by an authority.
If we start with a few basic observations:
- That we are part of a social species, and dependent on social interactions.
- That we are thinking beings, autonomous agents making decisions on how best to interact (theists and atheists seem to agree that we have choice, ignoring the free will derailment).
- That we are feeling beings, preferring pleasure to pain, satiation to hunger, etc.
- That we are empathic beings, able to feel how our actions are felt by others as well as by ourselves.
Then it would seem to follow that it is in our best interest -- and that of our families, social circles, and society in general -- to make decisions that maximize the well-being of ourselves and those around us. We judge such decisions as moral.
There is plenty of room even in this scenario to discuss how we rate competing values and thus competing senses of what is moral. For example, we can discuss the well-being of the individual versus the family versus the society versus the planet. We can discuss the relative merits and morals of short-term gains versus long-term responsibilities.