St. Paul never said to ignore people. He said, to brush the dust off and walk on, if people don’t accept their peace. No doubt, if those people came after him or other apostles and disciples, to join them, then they surely would not have not turned them away or ignored them.
Quite apt for the thread and our personal dialogue:
‘With all due respect’.
When people begin a sentence “with all due respect” what comes next is usually nothing resembling respect.
Paul never said to ignore people?

You obviously are ignorant of the bible. St. Paul said to shun certain people. Shunning is ignoring. Titus 3:10-11,* “As for a man who is factious, after admonishing him once or twice,** have nothing more to do with him**, knowing that such a person is perverted and sinful; he is self-condemned.”*
He also said that we are not even to have supper with certain people. That is ignoring people, I Corinthians 5:1,* "But rather I wrote to you **not to associate *
with any one who bears the name of brother if he is guilty of immorality or greed, or is an idolater, reviler, drunkard, or robber—not even to eat with such a one."
The Father of the Prodigal Son said his son was dead to him. That is ignoring, too. But, when the Father saw his son coming home (repenting) he accepted him with open arms.
So do we with those whom we may ignore.
It is a straw man fallacy to make the false argument of “No doubt, if those people came after him or other apostles and disciples, to join them.” as a rebuttal to this point. Those people coming after the apostle are REPENTING.
Obviously, we accept back the repentant. That is the one of the purposes of excommunication and the one of the purposes of ignoring people – to let them know their behavior is egregious enough to warrant the shunning in hopes that they will repent.
That is God’s economy. I do not care, nor does God, about your personal political correct nonsense opinions.
Learn your bible.
There is another reason to ignore people – to protect one’s own spiritual health and peace in Christ.