Don't underestimate the power of raw emotional reaction over the rational mind. There may be rumors that a tool like this exists, but if a religious insurgent hears the voice of God telling him to lay down his weapons, I wouldn't be surprised if he complied.
If someone is religious enough to attribute a voice with a god and obey it, just because they can't identify the source of the voice, surely they are just as likely to think it is a demon and disobey it?
