By this, love is perfected with us, so that we may have confidence in the day of judgment.…There is no fear in love; but perfect love casts out fear, because fear involves punishment, and the one who fears is not perfected in love.
John is not saying that no one should fear God's judgment. In fact, if you do not believe in Jesus Christ, fearing God's judgment is exactly what you should be doing. Jesus said,
He who believes in the Son has eternal life; but he who does not obey the Son will not see life, but the wrath of God abides on him. (John 3:36)
Much more then, having now been justified by His blood, we shall be saved from the wrath of God through Him. (Romans 5:9)
This is the true Gospel. It says, "The wrath of God abides on you. You stand condemned before God. Believe in Jesus Christ and be saved." In other words, the true Gospel sees fear of God's judgment as a necessary precursor which compels us to receive God's grace.
But there's a half-gospel that is taking over.