I think @grass raised a crucial point. we know it is possible for great people to go off both morally and intellectually. some prime examples that come to mind presently are: yochanan cohen gadol, Acher and korach. that is why chazal say” al tamin beatzmecha ad yom mosecha”. so let us raise the following question if great people can conceivably go off, what would have to happen for us to say yes this particular rabbi or gadol, he was great but he went off. Or maybe he became somewhat krum. he went in the way of Acher? I have an answer to this question but i will wait on it.
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