I'm an atheist. Although I was raised in the Christian church of my people, I slowly progressed to agnosticism in my teens and from there to atheism by my mid-twenties.
When my marriage began to approach its long-overdue end, my then-wife (not an atheist, but not a Christian either; she was basically ignorant on the whole subject) decided that we should join a church as a family - not necessarily to avoid the split, but so that we would maintain a family connection even if we got divorced. I didn't oppose the idea, although I did note that there were some churches that I wouldn't be willing to join. As it worked out, we ended up joining a local Unitarian Universalist church. I was fine with that, as they are explicitly open to agnostics and atheists (and pretty much anything else, as far as I could tell).
I rather enjoyed the church, even if I'd have preferred to have slept in on Sundays. It was nice to have a regular social event; my then-wife had pretty much kept us all clear of any social activities. The congregation were pleasant people, albeit mostly older, affluent, and white. There were enough children for several Sunday school classes, though. The doctrine was liberal and tolerant. I very much liked the open pulpit for "prayers and concerns"; I'm very comfortable with public speaking, so I went up when the spirit moved me (so to speak). I volunteered at the church library and as a Sunday school teacher. My son went to Sunday school and very much enjoyed it. He also attended the OWLS program and got a lot out of it. I joined the writing group at the church as well.
But there were things that bothered me.
It felt as if the one black family that attended the church were being, well, used. They were always placed in the first pew right in front of the pulpit, as if they were on display. They were asked to address the congregation from the pulpit almost every week. I couldn't shake the impression that they weren't entirely comfortable with that. What's more, the church spent two YEARS discussing putting up a "black lives matter" banner; much of the discussion focused on how to get the Mayor and the Chief of Police to attend the banner-hanging ceremony, and get maximum coverage on the news. At a meeting on the subject I couldn't resist pointing out that two years of discussion was two years of police shooting black Americans every day.
The church leadership often spoke proudly of the UU ministers and members who put their lives on the line during the Civil Rights era. If they'd taken the same incredibly long deliberative approach that the church leadership was taking about the BLM banner (I said), we would STILL not have civil rights - which we basically don't, anyway. The black family spoke up and agreed with me. But the minister and other leaders quickly shut that down. They accused me of being a radical, of demanding that they become a dictatorship by forcing quick decisions. I wasn't allowed to speak again, and no changes were made.
I started speaking at the pulpit during "prayers and concerns" about the many wars that our government was waging all over the world, bombing the innocent and helpless (including children) every day using our tax dollars. I received a few kind replies from elderly members of the congregation (basically old hippies), but once again there was no action. It became more and more clear that these were people who were there to congratulate themselves on their enlightenment and profound goodness without actually doing much about it. I used to joke privately that their arms were all sprained from patting themselves on the backs.
There were a few other atheists in the congregation. We had meetings about once a month. Again, they were enjoyable - but it felt as if the leadership and the minister kept trying to shoehorn us into the category of "humanists", rather than atheists. The minister dropped in to those meetings occasionally, and I couldn't help but feel rather patronized.
For all their proclaimed tolerance, they seemed uncomfortable with out-and-out atheism. On the occasions that atheism was mentioned at all during a service, it was ALWAYS in conjunction with agnostics and humanists - as if we were a single indistinguishable group. And I couldn't help but notice that although they had flags hung in the church with symbols of many faiths, there were none representing atheism - or even humanism, for that matter!
Eventually my marriage ended. My ex kept attending for a year or so, but then she met a Catholic man (the holiest felon and domestic abuser you could ask to meet) and she stopped showing up and dropped out of our lives. My son and I kept attending church for a while, but when he graduated out of Sunday school we both agreed that we didn't feel at home there.
So we stopped going. I enjoyed being part of a group, but I wasn't comfortable with what I perceived as their hypocrisy. Nor did I like being treated as a second-class citizen. If I could find an atheist "church" or a more sincere UU one, I'd certainly consider going. But as it stood, I wasn't comfortable in that congregation.
Oh, one other thing: I was a regular panelist at a regional convention for 25 years. I spoke on all sorts of subjects, but the most popular one (I think) was a series of panels I proposed for atheists and theists to talk and better understand each other. It was a wonderful experience; standing-room-only crowds, and a wonderful atmosphere of mutual understanding. But at one of the panels, the then-President of American Atheists (who was also on the panel) was offended when I mentioned that I attended a UU church. He called me an "Uncle Tom" atheist with considerable scorn. In fairness, he was promoting a book he'd just had published, a typical "new atheist" tome insulting Christians; my advocacy of dialog and mutual understanding was pretty much diametrically opposed to his thesis. But after the panel a number of members of the audience rushed up to me enthusiastically to support my approach.
It's amusing that both a hardcore atheist and "tolerant" progressive Christians were uncomfortable that an atheist would attend a church!
