Bingo! That's very very much what I learned growing up in mainstream Baptist churches. Of course, the sentiment wasn't quite so blatant or framed the way you're framing it.

We were taught that the closer one is to Jesus, the less one desires to sin.

People discovered in some kind of egregious sin, often sexually based, were described as backslidden and in need of a new commitment.

In other words, because they had sinned, they weren't fully Christian, even if they were still "saved."

I belonged to a church that believed you couldn't be unsaved, but the loophole they used to get around that was that some people who thought they were saved never really had been. They evidently hadn't had the "correct" amount of "faith" when they prayed the sinner's prayer.

And yeah, that definitely set up an attitude in the congregations I was raised in. Church-going Christians are the good people who mostly don't sin, and when they do sin, they repent and stop sinning.

Everybody else is "the world," unrepentant sinners Christian should not socialize with or even associate with too closely.

And so it goes ...