When I ask people who don’t believe in God to define what “Good” is I usually get something like this. “Good is that which helps most people live a good life. Something that benefits the species and keeps the species going.” For the most part that’s an okay definition. Though it’s too collective and subjective. Their definition wrongly equates “beneficial” with “Good.”
Let’s go into the hypothetical for a moment. Imagine nuclear holocaust happens. There is only one man and one woman alive. In order to keep the species going they must reproduce. Problem is that the woman doesn’t want to have sex. Would it be “good” for the man to rape and impregnate her to keep the species going? After all atheistic humanists contend that the purpose of life is to reproduce so the species continues.
One could make the argument that it would be beneficial to the species to do everything it takes to keep the species going in the above scenario. A sick argument. But one could make it. However, I do not believe that it would be objectively “Good.” It violates too many inherent values. The right for a human to live their own life as they choose. The value of the individual life. That which is objectively Good is not always beneficial. That which is beneficial is not always objectively Good. True Good I believe comes from God. Just like objective Truth. There must be a standard for Truth and Morality. I believe God is that Standard.