Originally Posted by Timstuff
Exactly. Sentinel Prime saw himself as a god over humans, and believed he had the right to enslave them. He was the one who taught Optimus that freedom is the right of all sentient beings, and Optimus knew that he was not the same Sentinel that he once knew and respected. He was a Decepticon now, and it was Optimus Prime's responsibility as the leader of the Autobots to destroy him. As long as Sentinel lived, humans would never be safe.
With the final Decepticon threat eliminated (Megatron, Starscream, Shockwave, Barricade, Soundwave, etc all K.I.A.) and Cybertron ceasing to exist, what could Sentinel Prime be capable of?
Optimus (along with the Autobots) and humanity could have powered down Sentinel, and imprisoned him for eternality for his crimes.