5. There's No Precedent For Them In The Original Series
This is perhaps the strongest reason to have The Enterprise Crew face off against the Borg. Sure, theres been non-canonical fiction where The Borg have been features or mentioned by Kirk & Co, but weve never seen any iteration of the classic characters encounter The Borg onscreen. This would be the chance, and theres nothing to measure it against. Much as I loved Star Trek into Darkness, who in the audience that had seen Wrath of Khan wasnt comparing the two? As successful as reinvention as Cumberbatchs portrayal was, we had seen the Original crew battle Khan in another timeline and it was spectacular, easily the best film in the Star Trek cinematic franchise. With The Borg, you cant really do the same thing because as good as First Contact was, it was far from perfect. So, a savvy audience are wondering how Kirk, Spock et al will react to an emotionless, domineering, relentless race theyve never officially faced before. The public will be treated to seeing a purely malevolent and sinister force that will be new to the uninitiated- Nero and Khan struck at the crews hearts, making it all personal. Khan kills Pike, Nero destroys Vulcan, etc. But The Borg have no concept of vengeance. They seek to assimilate and thats it. How the hell do they all react to The Borg, who have no agenda and see them all as subjects that must be turned? The Borg arent really a villain that fit any kind of philosophy Gene Rodenberry had with regards to the series when it started. They made sense as a new enemy for The Next Generation, as things became more violent, with a much less cocky Captain at the helm like Picard it made sense. Now that the characters and the universe Rodenberry created have been modernised and are a little less kitsch and retro, The Borg can be molded. In terms of story, they make perfect sense. In any Star Trek media, The Borg have always required a military response. Now that the seeds have been sown by Admiral Marcus for Starfleet to go off-course and militarise against the ever-present Klingon threat, how will that strategy evolve once a genuine threat is posed by The Borg? The Klingons are a warlike race who want battle, whereas The Borg could eradicate the human race by assimilation. How can that be anything but a plot worthy of a feature film?