Monotheism supremists have had a way of pointing the finger at themselves and calling one another a heretic. Divisions of beliefs within a specific religion tend to view one another as heretics for not believing exactly as them.

I see a lot of it as quibbling over minutiae of trivia. Pettiness. Personally, I don't think it matters if the father, son and holy ghost are three gods or three powers. Funnily enough, those who see you as heretical for believing they are 3 separate gods probably believe the same as you, they just use different words. They still believe in the father, son and holy ghost. They believe they are 3 separate powers. Call it a god, an entity, an incarnation. The differences are trivial, in my view. The same goes with the reverence of icons (saints), the act of which some Christian denominations view as heretical as well.