Summary: There is a need to return to the concept of shunning. Indeed, we should shun those whose politics are against Scripture even if they are called Brethren,
Having spent some time around Amish and Mennonites, I know they are pretty much the only groups that still practice shunning. Most are probably afraid of lawsuits, spitting the church or have a slightly off view of grace/love. We speak truth in love and some times we need to practice tough love and shun unsaved and saved alike. It is a biblical teaching.
2 Tim 2:14 Of these things put them in remembrance, charging them before the Lord that they strive not about words to no profit, but to the subverting of the hearers.
15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
16 But shun profane and vain babblings: for they will increase unto more ungodliness.
Too many times we forget these verses as we speak for the Lord and even politics on social media.
We also forget
Tit 3:10 A man that is an heretick after the first and second admonition reject;
11 Knowing that he that is such is subverted, and sinneth, being condemned of himself.
Long arguments with those in error only set you up for anger and frustration. If a person is not convinced or convicted after two corrections they will not be after two hundred. It is time to turn them over to God and walk away.
2 John 1:9 Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son.
10 If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:
11 For he that biddeth him God speed is partaker of his evil deeds.
When the cults come to your door, do not engage in long conversations. Do not let them in your house and do not offer any kind of blessing to them as you then become a part of their evil. You can say. "May God free you from your bonds and error" or "I will pray for your salvation" but even Goodbye is short for God be with you.
Rom 16:17 Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.
18 For they that are such serve not our Lord Jesus Christ, but their own belly; and by good words and fair speeches deceive the hearts of the simple.
If the doctrine is not right keep them out of your sight. Avoid them is clear. Note, you mark them or point them out for yourself and Paul called names so that others could avoid them and be aware of their errors. It is OK to call out heretics. It is part of the duty as a pastor who is called to protect the sheep from wolves in sheep's clothing. As a member of the family, we all have a responsibility to protect the family.
Just make sure they are a heretic either in doctrine or in some way dividing the Body of Christ. That could be by gossip, conspiracy or splitting a church for something other than doctrinal error or leadership failure. Leadership failure does not mean he preached against your pet sin or you disagreed with him. If you cannot prove it is error then you need to study and if necessary do Matthew 18's process for settling grievances.
What if a brother is walking in public sin or sin we can see?
1Co 5:11 But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
12 For what have I to do to judge them also that are without? do not ye judge them that are within?
13 But them that are without God judgeth. Therefore put away from among yourselves that wicked person.
This seems obvious, but I was offered a chance to preach in view of call at a church where the head deacon showed up at meetings drunk and if he did not like what he heard he went back across the street to fetch his shot gun. I declined. That is one of the problems with making people a deacon for life as it is hard to remove and defrock them. He should have done that one time only and been removed from his position.
2 Cor 6:14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
15 And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?