“Wisdom” and “fools” just don’t mix. After all, wisdom is “seeing life from God’s point of view” and the fool says there is no God (Psa 14:1). Not much common ground there!
Consequently, fools have virtually nothing of value to offer others and giving fools a platform to speak will be beneficial for no one. The proverb says anything they may say among “the assembly at the gate” will not be a good thing. If they do talk, somebody else will probably need to do some damage control!