In 1926, between the two world wars, Pope Pius XI instituted this feast of Christ the King. In so doing, the Church was making a statement that its members were to give their absolute allegiance to no government or person but only to Christ, the King of kings. Thus, we can see why this feast and Jesus' claim to be the King of kings may be controversial.
For example, when the wise men asked Herod: "Where is the newborn king of the Jews?" (Mt 2:2), "King Herod became greatly disturbed" (Mt 2:3). Before long, the village of Bethlehem was traumatized by Herod's murders (Mt 2:16). The mere mention of Jesus' kingship resulted in all hell breaking loose.
On the morning of Jesus' crucifixion, Pontius Pilate broached the subject of Jesus' kingship. He asked Jesus: "Are You the King of the Jews?" (Jn 18:33) Jesus claimed to be the King of a kingdom not belonging to this world (Jn 18:36). Jesus knew that Pilate knew He was the King (Jn 18:37), but Pilate refused to admit it and even questioned whether there was objective truth at all (Jn 18:38).
While Jesus was hanging on the cross, the controversy about His kingship continued. "The soldiers also made fun of Him," and said, "If You are the king of the Jews, save Yourself" (Lk 23:36, 37). The other criminal repented (Lk 23:40ff) and made the act of faith: "Jesus, remember me when You enter upon Your reign" (Lk 23:42).
Let us not be like Herod, Pontius Pilate, and the bad thief. Rather, let us be like the good thief and the wise men and women of the ages, who accept Jesus as their King on His terms.