Re: Optimus Prime's characterization (Spoilers)
Someone put it to me that he'd reached his limit... He'd seen his planet ripped apart through war... his friends all dying around him.
And then his long lost mentor turns around and brutally kills one of his few remaining friends and reveals himself to be in league with the Cons....
Prime had just had enough....
The plot to show Earth what would happen if they were gone was a bit...left field... but i wonder if they expected the hell to happen that did happen when they came up with the plot
*Insert clever, witty movie quote here*