Captain, I think it's a shorthand jargon term for 'has accepted the erroneous thinking completely'. I think the idea is akin to pod people in sci-fi stories, who have been 'taken over'. It's colloquial and colourful, and again, not really that helpful, and yes, I am seeing it more and more.
Verbeena, I still don't agree. Yes, people who present views that differ and are challenged do often back down and stop posting, which I think is a shame, but the robustness of the answers are no different in FWR to the ones in AIBU. It's just people feel bold enough to continue posting in AIBU, and for some reason there seems to be an element of tribalism in FWR, either in those who stay or those who don't and just post elsewhere on the site that they hate the place and hide all the threads.
There's nothing different in FWR to AIBU except the focus of topics. The moderation is the same, the software is the same. A thread was posted in AIBU and got moved to FWR and I was hopeful that, despite it's somewhat snide beginning, it could turn into a useful, engaged conversation, and it nearly happened, but the poster in question has stopped posting.
I can't help but feel rather bemused by this sniping from the sidelines about how nasty we are and how it's impossible to make your case when people just drop in, and then half heartedly bog off again.