Titus 3:10 is Scripture:
Titus 3:10 Reject a divisive man after a first and second admonition,
It is not appropriate to take everything through a Matt 18 approach. It has sadly been my experience that you are highly dependent upon very poorly prepared/trained church leaders who would rather endlessly try ministering to a psychopath than protecting his/her victim. Generally the victim has examined him/her self countless times, is very tenderhearted and almost beat down emotionally to a pulp. The psychopath has no care for anyone but him/herself.
Therefore, the church sees that the victim will try to follow everything they say (unto the victim's own destruction even) so they sin-level and throw the victim under the bus in their fruitless attempts to win the psychopath to Christ.
Quite often a victim is not safe to use the Matt 18 process. Titus 3:10 is the best alternative in many cases.