Looking at a page for
one of the Florida militias, it appears that they are fairly insistent about everyone being up-front in terms of identity and whatnot. That's completely understandable, to prevent nutcases and criminals from joining.
However, it may be asking a lot of certain people to join a militia group on anything other than anonymous circumstances. There may be businesspeople, public officials and people in highly competitive professional positions (and they bring their money and resources with them) who would be interested in joining - if it weren't for the potential of negative "militia group" publicity to bulldoze their careers.