I'm late to the party, but hey, they can: I'm an Atheist, and I'm fine with both, and here's why.
Old societies were built on Pagan values and beliefs, which covered all aspects of human life and activity. Christianism came, but it wasn't very good: too recent, too much of an empty shell, only covered belief in the afterlife, and a few values, mostly a code of conduct, but none of the countless aspects Paganism covered. The two met halfway, which led to Catholicism; others would rather say that Christianism itself is just an offshoot of European Paganism in the first place, but the point remains the same: the two retain the same values.
Atheism is the same thing. Oh no I don't believe in god nor gods, I don't believe in the afterlife, I don't care about all those things. But beyond the belief, there are values. I certainly care about those values, whatever their origin is. You are more right than you think when you say this:
Indeed, beliefs are just one thing, but they come and go; values are the common core we share, and they remained mostly unchanged throughout history.
I'm an atheist, but I'll keep celebrating spring as the renaissance of nature, as the coming of warmer, longer days, as the most prosperous time of the day- some will celebrate Easter, the renaissance of the Christ, others will call it Elaris Alba or Ostara, and celebrate the renewal of life. And as summer ends, I'll gather with my family and friends to renew our solidarity and prepare to face the harsh winter that comes, and spend good times together, what others will celebrate as All Hallows and Christmas, and others as 'Eluetias Alba, Samhain, Sol Invictus and Artuana Alba''. Those are just a handful of examples about holidays, but that applies to everything else: family values, work and art, men and women…
Granted, I'm not your average atheist, I remain a traditionalist, precisely because I realize how important those values are. The mistake most Atheists make when they turn away from religion is to reject everything associated with it, and as such, they turn away from its values, and end up as homosexuals, as sexually promiscuous people who disregard family values, on wellfare because they don't care to be a dead weight for their own society, as "open borders" retards who'd welcome anyone but their own…
Because I don't care what anyone believes, as long as they share my values. They're what made Europe so great at many points in history, while people turning away from it led to each and every downfall. We are already united, we just need to realize this common strength, and keep it intact for those values have come under violent attack by degenerates, who mostly rely on words like homogenization, equality, freedom, tolerance, and plenty other values taken from us and whose meaning was twisted.
Learn what those values are, and teach people the proper meaning of the words that represent them.