Opinions that do not proceed from the Truth are Foolishness and Destructive.
What is Truth? The WordOfGod is Truth and Jesus Christ is Truth. Joh 17:17 Joh 14:6
A Fool is a person who does not retain God in their Knowledge. Psm 14:1 Pro 9:10 Rom 1:28
Since our God, Christ Jesus, is the Truth, such people have no legitimate Foundation for their Opinions.
However, Fools are always quick to share their Opinions thus further Deceiving themselves and those who Listen to them.