Worse than this is the wide bunch of Christian sects, but at least they don't behead each other (anymore). First the Catholic Church, then the split into Roman and Eastern, then the split off of the various Protestant sects, way too numerous now to list.
I guess heresy and apostasy is an inherent feature of all religious groups.
Gibbon's description of the early Christian heresies in the Roman empire was entertaining.
The later, 13th century Cathars are a favorite of mine.