Mischief Maker wrote:

while Megatron's switch to the dark side made sense, the moment where the split between him and Optimus happens is really stacked in Megatron's favor. The whole movie they've been gorily ripping robots apart limb-from-limb, including comic relief moments, but in the final battle when Megatron's going to kill a robot who is basically a gential-mutilating Hiter figure, Optimus suddenly wants to spare Hitler, even though this Hitler works for their mortal enemies and will totally betray them again. The only thing they do to try and put things against Megatron is he misses one shot at Hitler and sends collateral rubble falling down on fleeing robots.