I feel like this is an oversimplification of Cicero's actual political power and machinations. He wasn't killed simply for his views. He was killed because he had been a public enemy of Mark Antony, having written many speeches denouncing him and rallying the people of Rome against him, as well as many in the Senate.

When Octavian made peace with Antony and formed the triumvirate with Lepidus, they went on a campaign of murdering all their political rivals to ensure that they stayed in power. Cicero was one of these because he had been so vocal in criticising Antony. He was killed for his political power rather than say, being like Socrates and simply for having different views.

The campaign of murder waged by the triumvirate against their political enemies is also another example of why the premier "Good Emperor" Augustus was not really a virtuous person by any means.

But the Republic of Rome that preceded the empire was not inherently more moral either. In fact by Caesar's time it had become corrupt and oppressive, and that's why the plebs loved Caesar so much because he improved their living conditions. The assassination of Caesar was not really (as is often portrayed) a heroic struggle against tyranny, but a group of wealthy oppressive people with generations of inherited wealth and power, wanting to destroy someone who was a threat to their status quo. For the common people, the Republic was more tyrannical than Caesar. It was only to the wealthy that Caesar was perceived as a tyrant.

I'm not saying Caesar was a hero but there are no easy narratives of good and evil in Roman history. In many ways Caesar was better for the common people than the Republic. And that's why his death caused such an outpouring of grief, which Antony and Octavian used against the Senate to eventually take power. And when Octavian became Imperator Augustus, he knew the path to sustained power was keeping the people happy by raising their living standards. Despite all his many flaws, he did that in very significant ways. But that doesn't mean he was a "virtuous, honorable person" that supported "freedom" the way we see it today. He used a lot of underhanded tactics to get and keep power.