Sure you can be good without God. Members of the SS could be good, as an example. Problem is they had a coherent point of view concerning the nature of personal morality based on culture, history, philosophy, and of course Darwinism.
There is a vast difference between a coherent point of view and an irrational ideology rationally engineered to appeal to people based on their common social identity, experiences, and insecurities. An inability or unwillingness to distinguish between the two underlies the allure of Nazism, Christianity, and any other highly ideological political or religious movement.
If you want to say you only meant atheists can be good in the sense they can act like observant Christians, I agree with that. You get into amusing territory at that point, though.
It is particularly amusing (though entirely predictable) that some continue to equate being a good person to living your life by selections from a book of 2000 year old campfire stories.
It is self-evident that religious belief is not required for ethical behavior. Attempts by apologists to "prove" otherwise are consistent failures built on misdirection and ad hoc fallacies. Some Christians are coming to this conclusion as well. Others remain in denial. Few of nonreligious are trying to force Christian supremacists to concede their self-proclaimed monopoly on benevolence, though. Zealots redefine reality at leisure to keep it compatible with dogma. No words will persuade someone that capable of self-delusion.
But non-believers always circle down the drain of their own convictions of social relativity at some point.
A little bit of projection there, Zed?