When to Divide for the Sake of Unity and Purity in the Church

Doctrine is one of the most divisive things in the church. What we believe Scripture teaches determines our understanding of God, the gospel, salvation, ourselves, others, life, and much more. Have you ever heard the saying, "There is no doctrine a fundamentalist won't fight over and no doctrine a liberal will fight for." You may not consider yourself a fundamentalist or a liberal when it comes to doctrine but if you are honest, you still lean one way or the other when it comes to doctrinal differences. Are you one that leans towards sniffing out bad doctrine and fighting over it for the sake of purity or are you one that leans towards unity at all costs and so allows any doctrine and practice into the church? In Romans 16:17-20, Paul makes it clear that there are occasions when we as a church are to divide from someone based on doctrinal error, but how?