Nah, I imagine anyone with purposes you listed would simply make a new fb account with not their photos to appear legit and post. It's easy. People going anon have legitimate reasons more often than not. For me personally, FB is the problem for not caring about people's privacy - why would it share my posts with all my friend list who aren't even in this group? I don't want to announce to whole world what I am planning or thinking about, it's such an invasion of privacy. If group was private, or you could select if you want your post shared to timeline, then I would have no problem posting without nickname.