It remains to be seen if this Optimus is an evil clone (which is more like the "Nemesis Prime" you've cited), or if it's actually Optimus Prime himself who no longer has free will and is being forced to attack his friends (which is what I referenced). It's too early to tell which it is (or if it's something different), but I suspect that it's the actual Optimus who's mind has been altered.
Okay, but that's a completely different issue from Optimus Prime doing evil things because he's been forced to. Because much like say the Winter Soldier, he's no longer his true self.
Also, the corruption of the Optimus Prime character that you speak of started in Revenge of the Fallen and has continued throughout Dark of the Moon and Age of Extinction. Basically, Optimus Prime in the first movie was the closest to his G1 persona, as evidenced by the fact that he was willing to sacrifice himself over killing Megatron by merging the AllSpark with his own chest. And he even cried out, "No, Sam!" when Sam shoved the Cube into Megatron's chest, then lamented over Megatron's remains ("You left me no choice, brother."). This showed the deep compassion and altruism in Optimus Prime. Someone who reluctantly uses violence. But in the sequels we see Optimus Prime take on a whole different persona, as evidenced in:
* Optimus Prime executing Scavenger (ROTF)
* Optimus Prime executing Sentinel Prime (DOTM)
* Optimus Prime threatening to execute Joshua Joyce (AoE)
But in AoE Optimus Prime's defence - and this is very important - he never carried out his threat. He had Joyce at gunpoint, but pulled himself back and walked away. Yes, Prime did kill Attinger, but this was not an execution. Attinger was an active enemy combatant who Optimus Prime killed in battle. And he had no choice because Attinger was about to shoot Cade. Although this Optimus did also enslave the Dinobots; literally threatened Grimlock with death if the Dinobots didn't ally themselves with the Autobots, and after the battle he emancipated them. You have to be enslaved before you can be emancipated.
Optimus Prime in the first movie captured the spirit of G1 Optimus Prime quite well, but Optimus Prime in the sequels was actually more like G1 Dai Atlas! (a character widely hated among Japanese G1 fans)