No one is saying that if one believes in God that one will be on the whole good and moral. I thought I made that clear: twice, now.
What I’m saying is that believing in God is part of being good and moral; it’s an integral part of it just as respecting life, being faithful to one’s spouse, and a bunch of other things is an integral part of being good and moral. Just because one is faithful to one’s spouse doesn’t mean that one is on the whole good and moral since one can be faithful to one’s spouse and also be a murderer. Likewise just because one believes in God doesn’t mean that one is on the whole good and moral since one can believe in God and do any number of immoral things. But both being faithful to one’s spouse and believing in God are part of being a good and moral person. That is, they are a necessary but not sufficient condition of being a good and moral person.
So while it can’t be said that if one is faithful to one’s spouse or if one believes in God that one is on the whole good and moral, it can be said that if one is an adulterer or if one is an atheist that one is not on the whole good and moral. Same thing with being a murderer. You can’t be someone who persists in mortal sin and be on the whole good and moral.
Being an atheist is worse than being a murderer. Comparing the two sins as if they were equal in gravity would be out of line since unbelief is a worse sin than murder. But that’s not what I was doing.
P.S. Murderers, just like atheists can do “good” things on earth. But that doesn’t make either of them good and moral people. Doing good things even many good things doesn’t make up for a fundamental moral failing of being a murderer or an atheist or an adulterer.