This plain was the scene of many decisive military victories throughout history. Entire theologies have been built around this single verse. A number of abusive churches create a fear of Armageddon, reinforced with guilt in order to dominate and maintain membership. Cults use this as a tool of emotional control. By implanting fear and creating guilt, abusive groups manipulate their members into performing free service.
Fear is the major motivator.
Guilt is a good enforcer, but it won't work unless you can make people feel guilty about something. We know God will destroy all wicked people shortly. Since we have knowledge of this we have a responsibility to warn others. If we don't do this God will find us bloodguilty at Armageddon. Cults need a bogeyman.