Contradiction with Romans 3:23
Romans 3:23 states that all have sinned, which contradicts the aspect of feeling sorrow for uncleanness and fornication in 2 Corinthians 12:21 because it implies ongoing sin rather than repentance.
Romans 3:23: For all have sinned, and come short of the glory of God;
Contradiction with 1 John 1:8
1 John 1:8 asserts that claiming to be without sin is self-deception, potentially contradicting the expectation in 2 Corinthians 12:21 for a community to repent from sin entirely.
1 John 1:8: If we say that we have no sin, we deceive ourselves, and the truth is not in us.
Contradiction with 1 Timothy 1:15
Paul identifies himself as chief among sinners in 1 Timothy 1:15, which might contrast with the concern in 2 Corinthians 12:21 where he admonishes others for sinning without remorse.
1 Timothy 1:15: This [is] a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief.
Contradiction with Ecclesiastes 7:20
This verse states there is no just man on earth who does good and never sins, somewhat conflicting with the expectation of repentance from sin described in 2 Corinthians 12:21.
Ecclesiastes 7:20: For [there is] not a just man upon earth, that doeth good, and sinneth not.