I went and read a little on him-- sounds like the big issue in his day was between people who thought icons were ok and people who thought they violated the commandment on graven images. Hmmmm. Yup, that's worth breaking communion over. NOT. (Although I know it's been done, over and over again.)
You don't think iconoclasm was a great and soul destroying heresy? OK. Here's what +Maximos the Confessor said about the heretical Patriarch of Constantinople when the latter espoused, along with the Emperor, the Monothelite heresy:
"Even if the whole universe holds communion with the patriarch, I will not communicate with him. For I know from the writings of the holy Apostle Paul: the Holy Spirit declares that even the angels would be anathema if they should begin to preach another Gospel, introducing some new teaching."
or this from the 1st-2nd Council of Constantinople canon 15:
"But as for those who...severe themselves from communion with their president, that is, because he publicly preaches heresy and with bared head teaches it in the Church, such persons are not only not subject to canonical penalty..., but are worthy of due honor among the Orthodox. For not bishops, but false bishops and false teachers have they condemned, and they have not fragmented the Church's unity with schism, but from schisms and divisions have they earnestly sought to deliver the Church."