1 John 2:27 tells us: "...you do not need that anyone teach you..." The context of the verse tells us that God Himself teaches us, and when someone teaches us to go against God, we are to turn away from that teacher.
It is a common thing for "teachers" to arise within Chistianity who tell us to disobey the many commands to love one another. They warn and explain that if we do not separate from Godly people who disagree with these teachers, we will become corrupted. We must instead become close followers of these teachers, reading and listening to no one except those whom these teachers approve of.
But God's Word tells us differently. It tells us that God Himself teaches us. If you follow Jesus closely, He won't let you get corrupted and ruined; He'll make you a fisher of men. And following Jesus closely means that you love all of God's people.
Php 4:21 Greet every saint in Christ Jesus. The brethren who are with me greet you.