Rabbi Sabbatai Zevi (1626-1676) was born in Smyrna in the Ottoman Empire and was a Sephardic rabbi of Romaniote (Judeo-Greek) origin who became almost universally recognized as the Mashiach (messiah) but was confronted by the sultan who demanded that he accept Islam or face death. As a token acceptance of Islam did Zevi in desperation take a turban on his head. His “conversion” was accepted. Later, rather than being forcibly converted to Islam was Zevi initiated into the Bektashi order, a denomination of core Median Judaism. Hundreds of his rabbinically Jewish adherents followed his example and accepted initiation into the Bektashi order. As the recognized Mashiach had Zevi naturally been initiated by the top poskim (rabbinic decisors) into the secrets of Esoteric Judaism, including the existence of core Median Judaism such as the Bektashi order and Zevi was perfectly well aware of what he was doing when accepting admission into Median Judaism in thus leaving the Southern Jurisdiction of Judah for the Northern Jurisdiction of Israel.
The scandal from the perspective of the top poskim as initiated into Esoteric Judaism was not only Zevi “acceptance” of Islam under duress, something which could easly have be reversed by him fleeing to Christian lands in Europe, but rather something far worse, as he carelessly and unintentionally exposed Median Judaism to the Muslims rulers. This in the minds of the top poskim could have exposed core Median Jews to the dangers of forced conversion to Islam and that justified excommunicating Sabbatai Zevi. In any case by not fleeing the Ottoman Empire and showing that the “conversion” was null and void had he in the eyes of the top poskim shown that he was not the Mashiach and was thus unworthy of leading the Jewish nation. His followers were summarily excommunicated along with him so as to not expose the Bektashis and the other six denominations of core Median Judaism. Protecting Median Jewry from persecution by political Islam was indeed paramount in the minds of the top poskim.