Re: Optimus Prime's characterization (Spoilers)
I don't mind Optimus killing Decepticons in battle. It's Optimus being an executioner that gets me.
Optimus talking to Megatron and Sentinal Prime at the end: "You will not stop until you rule in tyranny and humans are enslaved. I have read the humans' comics; you are the Jokers, but I am no Batman to let you have yet another chance" - BANG BANG.
Never really serious.
No thread is safe.