It's US who should be shunning THEM!
2 John is talking about the anti-christ. He describes it:
verse 7 - For many deceivers have gone forth into the world, persons not confessing Jesus Christ as coming in the flesh. This is the deceiver and the antichrist.
verse 9 - Everyone that pushes ahead and does not remain in the teaching of the Christ does not have God.and so concludes... verse 10 & 11 - If anyone comes to YOU and does not bring this teaching, never receive him into YOUR homes or say a greeting to him. For he that says a greeting to him is a sharer in his wicked works. Do I understand this correctly?