The link between God and morality and atheism and morality is heavily debated. Many ask if there is a link. Many more wonder if the link is strong enough to matter.
Morality as in justice, respect, the basic principles is one issue. The second issue is the content of morality. Eg abortion, stealing and so on.
Proving moral values are valid and true does nothing to prove that any of the content is convincing.
If you prove morality is objective, you cannot prove how morally bad murder is. You only get a "No"!.
This problem is worsened by the privation theory. It says that God does not make evil - but evil is rather only a lack of a good that should be there. A gap or lack tells us nothing about how evil it is. No matter how much a person does harm, you cannot prove that this is evil or a non-evil absence of good that might only resemble evil. Perhaps the person is possessed by evil and thus seems evil but is actually deluded by it and thus is not responsible. Evil needs correct diagnosis and the person must get the benefit of the doubt so proof is needed. The absence of proof and people acting as if they have got it when they have not, shows that evil is always in the person who points the finger.
It would not be surprising that if objective morality exists, that it rests on boring little arguments.
What if atheism instead of having no basis for morality actually has a little? That is fine if a little is all that is possible.