[ultima ratio]

Your logic is faulty. If someone gets his authority from God, he must use that power justly. If an authority puts an innocent man to death, he would be using his power unjustly and would immediately be delegitimizing his particular action. This holds true in all societies. It is never legitimate to wield power unjustly.

As for Romans 13, the way to read the text you've cited is to place it in its proper context. Paul is talking about governmental power and the need to obey it and not posit criminal acts. The laws of good order which govern most societies properly determine the behavior of subjects or citizens. But it would be perverse to take this to mean one could not resist injustice or tyranny or that governments could not do evil. When they posit evil actions, these may be resisted.

This is why your final point is absurd. Simply because authority is ordained by heaven, it does not follow power is always wielded wisely or justly. But the moment power is used in an evil way, such authority would over-step its divinely ordained mandates. Authority is given by God for a good reason--to assure justice and order, not to persecute the innocent. It is therefore always permissible to resist such evil actions--but never permissible to resist authority wantonly, for selfish ends.

[Inyokern]

As for Romans 13, the way to read the text you've cited is to place it in its proper context. Paul is talking about governmental power and the need to obey it and not posit criminal acts. The laws of good order which govern most societies properly determine the behavior of subjects or citizens. But it would be perverse to take this to mean one could not resist injustice or tyranny or that governments could not do evil. When they posit evil actions, these may be resisted.

Where does it say that in the New Testament?

Matthew 5:39 - But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also.

Jesus' message was that it was a sin to resist the Roman Empire. People who rebelled against Rome, such as Barabbas, are portrayed as criminals in the gospels. People who oppressed the Jews, such as the publicans, were not evil in Jesus' eyes. Jewish law could be ignored but Roman law should be obeyed, according to Jesus. The stewards of Jewish law, the Pharisees, were called "sons of the devil" by Jesus. Pilate, on the other hand, was faultless, according to him.

Perhaps Jesus should have applied for messiahship of Rome (which was what he really was).