The point has never been that an explicit belief in God is necessary to behave well, but that the notion of 'goodness' is meaningless in a materialist worldview.
If you're counting on death as oblivion, then why not go out on a killing spree? You lose nothing and will as a bonus, have you name remembered for decades to come.
It can work the other way around as well.Seems to be necessary for some people. At least by their own accounts, they'd murder, rape, steal, etc if they did not believe in an avenging god. I wouldn't call such people "moral" or "good" though. Just calculating.
If you're counting on death as oblivion, then why not go out on a killing spree? You lose nothing and will as a bonus, have you name remembered for decades to come.