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I guess the question is how far do they have to take things beyond the realms of the average christian faith in order to not be a christian faith anymore. It's like the question of whether or not Mormonism adds so much that it isn't Christianity anymore. Neither of these two are cults though, because to me a cult would require that it was self destructive at some point and to my recollection there is no moment of catholicism akin to "drinking the coolaide"
Some things that make me wonder if Catholicism is too different from Protestantism to be in the same faith are when prayers get treated more like spells than talking to god or the transubstantiation of communion, but regardless these questions only pertain to whether or not Protestants and Catholics are so different they shouldn't all go under the umbrella of Christian or if the definition should solely be about belief in Christ in which case Mormonism should be included which I don't think it currently is by most.
This is all based off growing up Protestant and attending Catholic High School for 2 years while currently being an atheist so I could just be misremembering some things.
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