No moral ground
All atheist moral systems fail what is called the grounding problem. You can argue at length about whether or not something is moral or immoral in a given example (for example the Trolley Problem) but when you come right down to it there are certain core things (like torturing babies for fun) that we all know are immoral but are not immoral for any definable reason. But we know they are immoral because we have a moral sense. This moral sense was inserted into humanity by God and without it there is nothing to ground a morality.
You will try to argue that atheists can be moral without God, but that is avoiding the whole problem. You are still obeying the morality stored within you, just denying that it was written by God. It’s a different problem.
Another way to look at this is that morality has an “ought” to it. It is something you “ought” to do. But agreements that lead to you “ought” to do something are always between two people, like when you promise to do something so you “ought” to do it. In order for morality to have an “ought” there has to be a being that you are in agreement with, and that being is God.
You bring up many interesting points. I’ll respond to them briefly from a moral atheist perspective, and will go into more detail if you leave any questions or thoughts in the comments for this post.
- My philosophy is grounded in logic. Logic is sufficient to demonstrate that it is immoral to torture babies for fun. No deity is necessary.
- That my feelings (what you call moral sense) agree with the findings of logic shows only that either evolved instinct, my culture, or both agree with this logic. You would have a better argument for divinely created morality if everyone’s moral sense agreed on all key moral issues.
- I agree that pointing out that deities are not necessary for morality would be avoiding your point.
- I agree that it seems to make sense that an “ought” should be a sign of an obligation to a person. In the context of atheist morality, I have an obligation to myself to be logically correct. That obligation leads me to a set of moral rules. If I violate those rules, I am harming the person I have an agreement with — myself.