The answer to your question is NO. Users can NOT ban you from posting on a GenForum.
The only person/people who can, are the administrators at Genealogy.Com. From what I understand, the only why they would do that is if YOU did not follow the Community Standards and Terms of Service listed at the top of these GenForums.
My suggestion would be for you do contact Genealogy.Com directly. Remembering that these GenForums are for User to User messages.