I hear or see this phrase entirely too often: "In my humble opinion..." comes from the mouths of Christians who are supposedly trying to tell the truth in an inoffensive manner to those who reject Jesus Christ and His Word. But, you know, there really is only one way to be truly humble: to submit oneself to the Authority of God.
Jesus said, "If you continue in My Word, then are ye My disciples indeed; and ye shall know the truth, and the truth shall make you free." Later, He said, "Ye are of your father the devil, and the deeds of your father ye will do; for he was a murderer from the beginning, and abode not in the truth. When he speaketh a lie, he speaketh of himself, for he is a liar and the father of it."
If you abide by lies, then you follow the devil, not God. Period. There is no way around that truth. You must find out the truth, if you would follow God. To say that you cannot know the truth for certain is a contradiction to the Word of God Himself, and therefore is not humble at all.
"There is no wisdom nor understanding nor counsel against the LORD" (Proverbs 21:30), and therefore those who contradict Him are not wise. That is the real reason that men don't acknowledge the truth--that they do not fear God nor follow Him. They are proud and need to be humbled with reality. Skirting the truth as if it is really not that important is folly on our part, as well as unloving, because these people will perish if they do not come to know the Way the Truth and the Life.