You simply send them a post card with your details. It's free to be an associate member, and $12 if you want to be their friend. http://www.theflatearthsociety.org/cms/index.php/about-the-society/joining-the-society
Well you seem to think the OP tackles the root cause... Hell, I'm not even arguing the article topic. I just think it could have been written in a more formal way. Would have come across more objective to its target audience and carried more weight other than coming across as a fan piece.