OK, I just checked again.
All the threads on the "Free for All" forum are locked, but now I can post under "New Topic", without having to register as a member.
I noticed yesterday that one of the members posted that the "Free for All" section wasn't accepting posts from "All", and asked whether this might provoke a legal challenge in his/her country (not the US, but I don't remember which one). I wonder what happened between yesterday and today.