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...
Really? I bet I've interacted with a lot more "Orthodox" Christians than you have and I honestly don't remember one person saying anything like this. Since when did calling someone a "fool" become the unforgiveable sin?
Matthew 5 is a warning about our attitudes. It states the person is "in danger of hell fire". A warning not a prohibition. It can't be a prohibition since Paul and Peter both call people fools and Jesus Himself called people fools in Matthew 23:17,19. Many of the OT prophets called people fools. The point seems to be to call someone a fool without grounds. Frankly, most of your exegesis of Bible verses leaves you vulnerable to that charge.
As someone else pointed out, this seems to be dealing with intra-church relations, the community of believers. I know that you dislike this conclusion but Mormons are not part of that group.
FOOL!2
Reading comprehension is not BIG in your life; is it?
22 But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
1. I ain't your BROTHER!
2. What part of WITHOUT do you not understand?
Uh...
It appears the wiggler is in your mouth; baited one!