The whole concept of 'heresy' is basically an argument between religious power brokers over who has control over a particular group of people.  

That's the common cry of both the Shi'ites and the Sunnis.  And they started their fight when Muhammed died over who his successor should be.  And that was almost 700 years ago.  

Heresy also gets substituted or replaced by apostasy, which is the explicit renunciation of one's religion, principles or cause, and blasphemy, which is an impious utterance or action concerning God or sacred things.

All are used to give or take political/religious power.  

See ISIS; the Thirty Years War in Europe, Excommunication, the Inquisition, Salem Witchcraft trials, etc. for examples.

Religion and theology and their priests/ministers/Popes/Bishops have killed millions 'in the name of God'.