Possible Missing Section
A query on GMF made me have a look at the Members Manuals; there is nothing there about members being removed for marking a message as spam. The Owners Manual does have a section about it, specifically 9.9.
People being "dismembered" is a fairly common occurrence so IMO there does need something in the Members Manual to explain it.
It is a more than somewhat complicated subject, and it might be worth you considering linking to the GMF wiki about it, at least as an interim measure.
Nina; I see that you have added a link back to the Owners Manual from the GMF wiki and that there is an FAQ item about the problem in the Help Centre (yes; I'm in the UK!) but links from the Manuals (both versions) back to the GMF wiki might help people.
IMO the FAQ is unlikely to the the first port of call for those affected; the manuals are a more probable destination.