"They believe what they were told to believe"
I don't remember that bit from either the movie or the book. Though admittedly I read the book a long time ago.
If that is an addon, that one line really changes a lot. The Fremen go from mystical warriors who see a great leader coming, CORRECTLY and thus get what they want, ,
to dupes of the bene gesserit, who use religion as a mechanism of control.