Heresy is the deliberate altering of the philosophy of the Holy Light and the departure from the traditions of the Church. Heresy is not simply a different belief, but it is the abstinent cleaving to error and suppressiveness to the Church. Those who are proclaimed heretics most generally are not hunted by the Church of the Holy Light. The most severe punishment is excommunication, which is a lifting of the Church's protection, but not all heretics and schismatics incur such a penalty.
The Argent Dawn believes the church’s old methods of dealing with evil no longer suffice. Evil constantly changes and refines its methods, and the Argent Dawn believes that the good must also change. This is against the belief of the Church that the good must not be appropriated and that it does not need to be appropriated. An example of this belief in practice are the strange sacrificial rituals which Argent Templari oblate in order to receive their power.
The Argent Crusade, though widely regarded as heretical, has not explicitly been condemned by such. Hard-line churchmen cite Tirion Fordring's usurping the title Highlord from the authority of the Church of the Holy Light and the continued secession.
The Scarlet Crusade takes appropriating the good to the next level. The Crusade has sold indulgences to fatten the coffers of hierarchical figures, a practice strictly prohibited. The Crusade also practices torture, a practice the Church is obstinately against. The Scarlet Crusade is considered to be secessive from the Church of the Holy Light.
The Church of the Holy Light explicitly condemns the actions of the Blood Knights against the Naaru. The Church also preaches against the Dominion of the Sun, a group of Blood Elves known for sacking temples. There is an open agreement for Blood Elves to enter the Church of the Holy Light away from their apostatic brothers.
The Cult of Belore, in its purest form, believes the Holy Light is subordinate to an anthropomorphic sun god, Belore (Thalassian cognate for "sun"), who is the source of divine magic. It is a belief that its few modern benefactors claim is ancient and indigenous, but archaeological record has no attestation to this claim. The Church disputes that this Belore heresy is idolatrous sun worship, a nationalistic elven take on the Deus heresy. Recent efforts have tried to syncretize the two beliefs, but the Church remains firm in its denunciation of all forms of sun worship.