Maybe it’s not that they hate everything that isn’t G1, but they just don’t think Optimus Prime needs to have a mouth. I, for one, think he looks cool with the faceplate on, and it doesn’t need to be a “battle mask.” It should just be what his face looks like. And if you think it would look “incredibly stupid” for him to have a face plate on all the time, then that’s your opinion, but I must say that I strongly disagree, a huge amount of other people also would likely disagree, and so would the 20+ years of various Transformers shows that have existed before the movies, plus the 13-year-long run of the IDW comic universe, all of whom have given OP a permanent face plate. And nobody associated the faceplates with “battle” until the movies started associating them together. Trust me, if two robots were beating the shit out of each other, the audience would easily be able to distinguish that it is indeed a fight scene, wether or not one of them has a mask covering his face. Also, I know other people beat me to it, but I also would like to weigh in on the whole “true intentions” thing: emotions and their expressions are all in the eyes, not the mouth. Sure, you can smile or something, but you can easily tell if someone is genuinely smiling by looking at their eyes. As for characters in the movie, if they see a giant robot, they will likely be afraid of it. Wether they see its mouth will not be a factor. Finally, I’d like to point out that it just doesn’t make sense to have the battle mask in the first place. If your entire body is made out of metal, what is the point of another piece of metal? Not to mention the fact that it only covers his mouth and the bottom of his nose. Where’s the protection for, you know, the rest of his body?