This may not be exactly your fix, but the way I got this to work during my testing was to give Registered Users edit permission to the module.  Now all registered users can contribute to all unrestricted (not private) and unmoderated forums just fine.  However, this REALLY confuses the heck out of me...  Why put a setting in Forum Administration labeled "Authorized Edit Roles" and in the documentation say that this is the way to allow users to post, if this isn't entirely the case.  My "Authorized Edit Roles" is now empty, yet everything is working like I expect it to.

Keep in mind, this is only preliminary testing, so I am unsure if what I have done is a security risk, or if it is the correct thing to do.  But it indeed worked for me (so far).  :)

Yes... That has been figured out, but why have a setting in the Forum Administration called "Authorized To Edit" and then in the documentation tell people to use this setting to allow them to post to the forum?  Does anyone know what that setting actually does?