Bridging the Gap Between Believers and Skeptics
... but not about why it hooks people.
People join a religion for the same reason they join any organization. They want to feel involved and be part of a community.
When I joined my Unitarian chapter I ended up going to Sunday services, and participating in YANKS and Chalice Circles while I lived in Milwaukee's east side. I still remember the times we'd offer each other hands as we did congratulation ceremonies. Despite the individualism of western society it does feel good to be part of something larger than yourself. Even an atheist like you could be a Unitarian by the modern sense of the term. UUism as it is designed today is supposed to be a religion without walls, and I also know you are politically progressive, and would uphold UUs own progressive values.
When I joined the Baha'i Faith I found out that there were about 500 Baha'is around Milwaukee, but only one-tenth of them, or fifty, were active. Despite having very spiritual roots, I find the Baha'i Faith in general to be kind of a DIY religion, especially since how their prophet often stressed the "personal investigation of truth", well, as long as it doesn't break what the Baha'is already know and understand about God. Baha'is in my area often meet in libraries and in public parks, and often read scripture and try to help each other understand the full context of what Baha'u'llah was trying to convey.
I am now a lapsed member of both religions, although I often get both Unitarian and Baha'i material sent to me through the mail, because I am a member of both. I've tried to contact the official Earthseed organization, but unfortunately, there hasn't been any formal declaration that I belong to that organization. Yet still, I am RF's leading Earthseed advocate, often preaching and advocating for pantheism and syntheism. So, even though I've never undergone any formal recognition of such, my heart, body and soul is much more part of Earthseed and what it represents to me than the other two religions.
So yes, I am a lapsed member of two religions, Unitarian Universalism, and the Baha'i Faith, but I actively engage with and practice Earthseed, and have since I was 14. Had I know about Earthseed before the other two religions, I most likely would have never joined the other two. The other two were just there as placeholders until I found a religion that I happened to actually agree with.
... and here we are, finally. It wasn't until my 30s that I discovered Earthseed, but now that I found that other people came to the same realizations as me, I'm never turning away from it. Finally, I discovered an organization that believes the same core values as me.