As you observe, there is no reason in principle why an atheist can not live a good and moral life - and no doubt some or even many do.
But in practice the only atheists I ever run into are the ones who sneer that religious people - of any sort - are by definition stupid and morally degenerate. These, I find most tiresome.
“No one laughs at God”
when.....
Regina Spektor - “Laughing With”
https://www.youtube.com/watch?v=-pxRXP3w-sQ