Not really DU, reread your own post and the scriptures quoted there in, paying special head to the term brother.
Then remember there are actions and guidelines that apply to the family of Christ and the brothers and sisters there in.
Then there are actions and guidelines that apply to the lost and confused...
Then there are those that apply to those outside, those who attack or attempt to subvert the family and the Savior...
By their very nature those who deny the real Christ or worse bring people to a false gospel are by their own acts rather foolish (or cunning depending on motivation).
Of course we still hold out hope, for Christ, the real one, is always waiting for the lost or those who never knew him to begin with...