The pope is not a god. He cannot order the destruction of God's Church. His whim is not the law of the Church. In fact, its laws and precepts are the reason for his authority in the first place. He is given power precisely to sustain them and to protect the deposit of faith. He cannot do as he wishes with his subordinates, without just cause. In this he is subject to Church canons, as is anyone else, since they are based on Divine Law. He must therefore act justly, not as a tyrant.
We say the pope is supreme. But what does that mean? We say the Supreme Court is the supreme law of the land also. But we don't believe the Supreme Court has a right to act as it pleases, to depart from its own limitations, to act as chief executive, for instance. We recognize in the word "supreme" certain limits. So too with the pope. There are limits to his authority. He abuses his power when he exceeds these limits--as he would if he acted unjustly.