Facts.
Either that or methinks you don't know what a real tyrant is.
A tyrant is someone who uses the power of the state to have a man with whom he has a theological disagreement executed.
It is you who is making an attempt at historical revisionism. Calvin (for all his good qualities) died with Servetus' blood on his hands. That is a fact.
I'm sure this makes perfect sense to you in the comfort of your 21th century PC culture.
However, Calvin lived in age when men believed (correctly) that it was the magistrate's duty to uphold both tablets of the Moral Law of God, that is, the Ten Words.
Your friend Servetus was already convicted of public blasphemy and heresy, etc in other civil jurisdictions. He fled to Geneva hoping to escape execution, which is what his public crimes deserved. The civil authorities in Geneva would not have any of this, and with the aid of Calvin as prosecutor, they put your friend to death.
So, you may examine the case to see this was not merely a matter of “theological disagreement” (e.g., red wine vs. white), but a direct violation of the Ten Words, which used to hold sway in both the civil and ecclesiastical realms until the Church and State in the West became infected with Enlightenment humanism.