The Bible clearly instructs us to keep away & not to mix with a “Christian” (note the word ‘brother’ in the verse below) who has any of the traits below:

“and now, I did write to you not to keep company with him, if any one, being named a brother, may be a whoremonger, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner — with such a one not even to eat together;” (1 Corinthians 5:11)

How about “non – Christians” who behave such?

Two verses prior (to the one quoted above), we find the answer.

The verses (below) clearly ‘allow’ us to mix with “them” (note the phrase “of this world” = non – Christians) Here they are:

“I did write to you in the epistle, not to keep company with whoremongers — and not certainly with the whoremongers of this world, or with the covetous, or extortioners, or idolaters, seeing ye ought then to go forth out of the world —” (1 Corinthians 5:9 – 10)

Quite the contrary is often taught in many churches today.

P/S:

Why and what’s the logic to this?
The concluding verses from this ‘same’chapter reveals it:

“those inside” = Christians = we judge by keeping away and not mixing with them if they behave such.

“those outside” = non-Christians = we don’t judge because it’s not our business to do so; God will judge them.

Here are those concluding verses from this ‘same’ chapter which speak this ‘truth’:

“What business is it of mine to judge those outside the church? Are you not to judge those inside? God will judge those outside. “Expel the wicked person from among you.”.” (1 Corinthians 5:12 – 13)