I don't know of a mainline Protestant denomination that DOESN'T believe in the Trinity. And they're not all heretics. Some hold heretical beliefs, but others are merely in schism.
Go understand “quantification” before you debate with the big kids.
That Catholics are polytheists, but somehow other Christians that “have the exact same belief” in the Trinity are not. Mutually exclusive.
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Cahtolics are not polythiests as far as the Trinity is concerned. You could put the Pope and Jerry Fallwell in a room and when it came to the Trinity they would be in exact agreement.