Contradiction with Matthew 5:44
John 9:28 shows hostility towards Jesus' disciples, but Matthew 5:44 encourages loving your enemies and praying for those who persecute you.
Matthew 5:44: But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
Contradiction with Romans 12:14
John 9:28 involves cursing and reviling, while Romans 12:14 instructs to bless those who persecute.
Romans 12:14: Bless them which persecute you: bless, and curse not.
Contradiction with 1 Peter 3:9
John 9:28 involves insult and reviling, yet 1 Peter 3:9 advises not to repay evil for evil or reviling for reviling, but to bless instead.
1 Peter 3:9: Not rendering evil for evil, or railing for railing: but contrariwise blessing; knowing that ye are thereunto called, that ye should inherit a blessing.
Contradiction with Proverbs 15:1
John 9:28 includes harsh words leading to strife, whereas Proverbs 15:1 advises a soft answer to turn away wrath.
Proverbs 15:1: A soft answer turneth away wrath: but grievous words stir up anger.
Contradiction with Ephesians 4:29
John 9:28 has corrupt communication, while Ephesians 4:29 advises against corrupt speech, suggesting words that uplift.
Ephesians 4:29: Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers. [to...: or, to edify profitably]