I went to an atheist "church"

[Mister Agenda]

I can't imagine the Unitarian Universalist church I belonged to in the late 70's early 80s would have the slightest problem with atheist members.

And even then, the extremely non-standard theology would scarcely chafe most of the atheists here today.  The pastor had a unique view of God:  go break a tea cup.  Now tape it back together.  That's God.

they had so diluted the 'message' and embraced so many different doctrines from around the world that the net sum was zero, LOL.

To their credit, they were very supportive for any members going through anything adverse or untoward.  Just totally non/poly/multi/un-doctrinated in how they do it.

We did a survey some years ago at the UU I attend and it came out about 50% Humanists, 25% atheists (who were probably mostly in the Humanist camp). About half considered themselves some kind of theist, but that included Christians, Jews, Buddhists, and Pagans.

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Sunday service and Sunday school for kids...

Hm, for people who supposedly hate religion, they sure do like copying us. 

You don't own meeting and socializing and you don't own Sunday.