Contradiction with James 3:2
James 3:2 indicates that all men err in their words, while Proverbs 17:7 suggests that eloquent speech is not fitting for a fool, implying that fools should not speak eloquently at all.
James 3:2: For in many things we offend all. If any man offend not in word, the same [is] a perfect man, [and] able also to bridle the whole body.
Contradiction with Proverbs 26:4
Proverbs 26:4 advises not to respond to a fool according to his folly, distinguishing how to interact with foolish speech, contrasting with Proverbs 17:7's idea of how speech decorum is unfitting for fools.
Proverbs 26:4: Answer not a fool according to his folly, lest thou also be like unto him.
Contradiction with 1 Corinthians 1:27
1 Corinthians 1:27 states that God chooses the foolish things of the world to confound the wise, suggesting a valuable use of the "foolish," whereas Proverbs 17:7 implies a negative connotation to fools speaking eloquently.
1 Corinthians 1:27: But God hath chosen the foolish things of the world to confound the wise; and God hath chosen the weak things of the world to confound the things which are mighty;
Contradiction with Proverbs 8:5
Proverbs 8:5 encourages the simple and fools to understand and be wise, suggesting they can elevate their speech and understanding, contrary to the limitation expressed in Proverbs 17:7.
Proverbs 8:5: O ye simple, understand wisdom: and, ye fools, be ye of an understanding heart.