The idea that Megatron would choose to wear the Autobot insignia, to fall in line with the people who've been impeding Cybertron's progress all along, to follow Elita -- that's easily worse than if he'd been coerced into it somehow.

"I don't presume to understand," Starscream says shortly. Because this is utterly absurd. He's starting to wonder if space bridge flare knocked him back with a concussive blast, and if this is all some extremely discomfiting dream. "And I'm not here to make trouble. Frankly, I'd rather spend as little time on this ship -- the Lost Light? -- as possible. All I'm concerned with is getting back to Cybertron. My Cybertron."

He means it as a kind of biting insult at what considers to be fraudulent nonsense, but then he's forced to fully entertain the possibility that this isn't his Cybertron, his world, and that this is actually Megatron, in a manner of speaking, and that the space bridge did a hell of a lot more than just jettison him off to some random coordinates. With the nature of spacetime and the very specific ways space bridge theory manipulated it, there was just the slightest possibility that this was actually...oh no. And the "oh no" shows on Starscream's face pretty clearly.