Afellow – that is true in most cases, but in instances where one aide disputes the total legitimacy of the other, that attitude is misplaced. There were full fledged rabbonim in Europe who were maskilim; they had left normative Orthodoxy and even though they were knowledgeable, they were not reliable poskim. This list includes some names that I’d rather not mention, but is known in the deeper circles of the yeshivishe world. Chasidim never acknowledged them to begin with. Other examples of this phenomenon are people like shmuel Dovid lutzato, who kept the mitzvos but was very influenced by haskalah and was therefore shunned by the frum world.
So too with orthodox rabbis who allow female ordination; some established religious zionist morei horaah such as the author of bnei bonim have endorsee it – his rulings are to be disregarded entirely; he us unfit to render halachik rulings.
Many gedolei yisroel felt that chabad had taken such a turn in their own way.