Never Read the comics...but the Autobots are supposed to be life loving robots (I know ironic huh?).
I don't know that "life-loving" is really the right word. To be certain, their primary goal is the defense of the Human Race, and they've taken in Decepticons who jumped ship and switched sides. At the end of the day, though, they've destroyed Life in the name of protecting the innocent multiple times; even in the original series, you have episodes like "Kremzeek", where even as one Autobot, Bumblebee, raises concerns about finding a non-violent solution, the Autobots ultimately decide to terminate an entirely new, seemingly-sentient life-form because of the threat it poses to the rest of the Planet.
Even in the Movies, though, I don't think it's fair to say Optimus "butchers" his enemies. Taking into account how big and powerful ALL Transformers, Autobot and Decepticon alike, show themselves to be, and how intense each and every battle becomes, at least to me it feels clear that whatever extremes Optimus goes to during the Fight are made understandable by the facts that
every attack all combatants involved deliver could prove to be the killing blow and so, when the opportunity to deliver such a blow presents itself, one cannot afford to ignore it.
I'm not about to pretend I'm 100% comfortable with that myself, mind you, and I
definitely feel like, under those circumstances, the films could afford to cut down on Optimus' in-fight dialogue. I just also think it's not as starkly "out of character" as some would have it.