Contradiction with Proverbs 10:11
Proverbs 10:11 states that the mouth of a righteous man is a well of life, which contrasts with Proverbs 12:6's indication that the words of the righteous may not always bring safety or life, as they are needed to deliver from the wicked's speaking of violence.
Proverbs 10:11: The mouth of a righteous [man is] a well of life: but violence covereth the mouth of the wicked.
Contradiction with James 3:10
James 3:10 highlights the inconsistency of the tongue, where blessing and cursing can come from the same source, contradicting Proverbs 12:6's dichotomy between the plans of the wicked and the deliverance by the righteous.
James 3:10: Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be.
Paradox #1
Proverbs 12:6 suggests that the words of the wicked intend harm, while the speech of the upright brings safety. A possible moral inconsistency here might be that not everyone who speaks harmfully is necessarily wicked, and not everyone who speaks in a righteous manner is always good. People's intentions and morality can be more complex, and judging them solely based on their speech might not account for their entire character or circumstances.