1 transformillion year sentence in robot jail

To be clear: Megatron is a fascist. This isn't something he slowly formed into over the course of the war, it's how he started it. At some point he personally believed in a route that followed pacifist, collective reform, but this was never his true party line. Megatron didn't envision a world where the subjugated were free from their hierarchy, he envisioned a world where he was on top instead.

Quoth Towards Peace: '...your "betters"? You have none. We are all equal. And we have a right to decide how to live our lives.' This is notably not, and never was, how the Decepticons were organized. Hearing it straight from Megatron's mouth, one might believe this is completely at odds with what they become in the future, but that's exactly what he wants his listener to believe. Here's one of my favorite moments in all of IDW:

Over and over again, he says us versus them. He doesn't specify who 'they' are, because the point is that the listener can fill that image in with their own personal grievances. He wants them to believe, as Drift says, that there is no other way. He does not believe in equality. He poses the Decepticons as the "betters" instead— the strong, the powerful, the just; they are the true voice of Cybertron, the real heart of this nation. The way Megatron speaks eliminates any shade of grey from their world. There is only us and the enemy, and the enemy is both infinitely powerful, oppressive, and infinitely weak, pathetic. Never mind that there are people within the system who seek to change it for the better, like Orion Pax, never mind that there are people on the streets already fighting for it, like Hot Rod. There's only with Megatron, or against him. And if you are with him, you are stronger, more noble than you have ever been.

Believing that Megatron's voice is the only one speaking for justice in IDW1's pre-war Cybertron is falling for his charisma. The Decepticons were never the 'good guys'. Megatron used the pain of his people as leverage to put himself in power...

...and if they're brutal, cruel, it can only be the fault of the system. The Decepticons didn't make themselves that way.

...if they're selfish, deceptive, it's only a failing to hold close enough to their zealotry. There is nothing wrong with the heart of the movement— the true heart of Cybertron.

A real Decepticon is always just.

The Decepticon Cause meant something different to every person who believed in it. But the Decepticon army exists with the singular purpose of war, of which the singular purpose is control. Megatron is ruthless, nationalist, anti-religion and anti-compassion. He pretends his expansionism is defense. His vision for the future is freedom only for himself.