You can call them a fool, if there is no fear of God in their heart, if they say, “There is no God.”
You can call them a brute beast if they are fit for destruction, if they live their lives in purposeful pride, vainglory and for selfish ambitions.
You can call me foolish if you so desire. “For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.” (1st Cor. 1:18) But if the words offered can be verified as truth from the Scriptures, and there is the wisdom of God in them, then I will not be moved, no matter what.
“My help cometh from the LORD, which made heaven and earth.” (Psalm 121:2)
But do not call people stupid.
It does not matter if their actions, words or deeds, if their lifestyle or choices are indeed stupid, if you say so to them, more than likely you will lose every opportunity to witness to them, and there is a possibility that their blood will be required at your hands.
It matters little the type of person you are speaking to, if you know that what they are saying is incorrect, and you offer them truth, their defensive mechanisms will immediately be put up. One who has studied humans can almost instantaneously recognize this attribute, a shift in posture, in their demeanor, their verbal exertions, they will in one way or many, rebuke your offering of the truth.
In the bluntest of terms, our responsibility is to reveal to those we meet who do not serve the Lord Jesus Christ that they will never be good enough in His eyes for salvation, that not one word or deed they have ever done or ever can do will allow them entrance into the Kingdom of God. We do so as lovingly as possible, and some do indeed respond to the conviction of the Holy Spirit, you did.
Others though are fools, they are brute beasts, they are reprobates and bastards, and they will refuse everything you say. You can continue to kick against the goads if you so desire, with some, those that you call family and friends, for your entire life if you so choose, but with some it will avail you nothing.
“What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:” (Romans 9:22)
Are these people stupid? You bet they are, stupid beyond all comprehension, but only those who have been crucified with Christ know this truth. It is beyond stupid to deny the love the Lord offers when one has been told the truth of the pit of despair that awaits all that do so. It is stupid to reject the sacrifice of the Lord Jesus Christ as sufficient within itself as acceptable to the Almighty. It is stupid to believe that dust can add anything to the cross that the Living God will accept.
Stupid people live their lives as if there were no God, the Word of God says, “The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that doeth good.” (Psalm 14:1)
Stupid people live their lives solely for themselves. “But these, as natural brute beasts, made to be taken and destroyed, speak evil of the things that they understand not; and shall utterly perish in their own corruption;” (2nd Peter 2:12)
Stupid people deny Ephesians 2:8-9. “For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.”
But never call them stupid.
“And others save with fear, pulling them out of the fire; hating even the garment spotted by the flesh.” (Jude 1:23)
To deny the gift of eternal life, through faith in the Lord Jesus Christ, the free gift of salvation given by the grace of God to all who believe on the name of our Savior is beyond stupid.
In every conversation, do all that is possible to keep them from putting up their defensive mechanism.