Heresy can be rooted in a false doctrine or the rejection of sound doctrine. The term has a meaning that involves 'choosing' through a process of being subverted or 'twisting out' of the truth. If I, as a believer, am not taught sound doctrine on a consistent basis (daily) by a qualified pastor/teacher that God has raised up, I will be susceptible in relying upon my own understanding and personal experience of truth and develop diverse opinions of who God is and how he works. This opinion is chosen and twisted out of an acknowledgment of the truth but not the knowledge of the truth. This form of sublimated truth has nothing to do with the believer's faith. It can be very convincing to the untrained ear that is not skillful in the words of righteousness. Legalism is a form of heresy that brings others into bondage because it rejects mercy and grace. These heresies cause division and factions that leads to taking advantage of others with potential ruin among those who are not yet rooted and established in the faith.
We can not randomly attribute heresy to others who we do not agree with or who seem to have a different understanding of truth. It may be some form of false doctrine but we must entreat them and not accuse them. If they are persistent and become resistant when we have entreated them through meekness and much patience, then we can admonish them so that they will not effect others. If they reject a second admonishment, then we can reject them and warn others of their heresy. This is a process and not a knee-jerk reaction unless this has been a practice by the individual or group.
We can not randomly attribute heresy to others who we do not agree with or who seem to have a different understanding of truth. It may be some form of false doctrine but we must entreat them and not accuse them. If they are persistent and become resistant when we have entreated them through meekness and much patience, then we can admonish them so that they will not effect others. If they reject a second admonishment, then we can reject them and warn others of their heresy. This is a process and not a knee-jerk reaction unless this has been a practice by the individual or group.