Hasn't this Autobot become what he hates ? In mercilessly executing a Decepticon begging for his life, hasn't he crossed the line and become a selfish murderer, himself ? Did he not choose his own vengeance over justice ?
Devil Gundam wrote:To him, this is justice. He may be doing Decepticon like things but he believes that one must fire with fire, in a sense.
Besides we have seen Autobots willing to give no mercy before, see the original movie when Prime was ready to kill Megatron, despite his begging for mercy.