atheistdiscussion.org, although most of the recent activity there seems to be in the political arena, there's been a lot of discussion of religion / [a]theism including a ... shall we say ... "vigorous" stem-winding thread about the historicist vs mythicist debate. This is the user-funded resurrection of what was formerly the discussion forums on thethinkingatheist.com, which were unceremoniously closed a few years back.

atheistforums.org (and IIRC there's an unrelated atheistforums.com)

[city-data.com] atheism & agnosticism forum has some interesting discussion but they're heavily moderated. No straying from thread topics as even organic topic drift is seen as derailment, no bringing up or discussion of science in that forum or religion in the science forum that they also have, etc. Almost no swearing, etc. If you can hold your nose and type around that nonsense, there are occasionally interesting discussions and a handful of really good posters there.

There are a few, and the number is growing.
There are support groups for those leaving or having left specific cults and organization like the FFRF and Atheist republic.
Though sadly this place too is developing its quota of self righteous censorious busy bodies, who would muzzle the "wrong sort of atheists" give the opportunity.