I wonder if the REAL villains are these Klingons... perhaps they attacked Earth first, and "Harrison" is a secret but illegal weapon unleashed to bring hell upon them, not in the name of the Federation, but Earth itself, making him a nationalist conundrum: Do you trust Starfleet to save us, or does the private sector do it themselves? (and make a bit of coin to boot). Perhaps the character that Peter Weller plays is the Peter Weyland of Trek who keeps the banned Khan inspired eugenics project going secretly. Harrison, (a Starfleet officer?) is recruited bent on his own personal blood lust (maybe earlier dealings with the murderous Kilingons) make him the ultimate volunteer for this "super solider" program. He takes them on as a one man eugenic army to destroy the Klingon threat in a way Starfleet can't ... But Kirk and Starfleet gets in the middle, holding the thin, prime directed, line faithful to what the Federation stands for. And making Harrison a morally ambiguous character as the human future of alien warfare in an increasingly deadlier galaxy that Starfleet may not be ready for. Especially after the events of Trek09 and the destruction of half the fleet and all of Vulcan.
To be honest, I've started to wonder the same thing. To me, in the trailer at least, it almost seems as though Harrison is saving Kirk and co. from the Klingons.