Perhaps they decided to separate because the Scriptures demand, although sometimes that demand is seen by some sooner then others.I was adressing those who have proper theology, and then also decided to separate themselves from others due to not being "of like minded faith".
An example may be the decision of no longer endorsing Billy Graham. Some recognized the chase to embrace modernism much earlier then others. But ultimately those who were theologically sound had issues with him.
They may not have separated, but neither were they wildly enthusiastic.