1. Time Travel
Oh, don't get me wrong, I love me a good time travel yarn. Time travel stories are eternally appealing to virtually everyone because everyone has at least one thing in their past they wish they could go back and change or do differently. For instance; kind of wishing I wouldn't have gotten those Asian Zing wings at Buffalo Wild Wings for lunch right about now. However, once you open that door in a fictional universe, it should change everything in such a radical way that it's never the same again... and yet, everyone eventually shrugs their shoulders and goes on their merry way. To be fair, Star Trek opened up that door long before First Contact as far back as TOS (and went to that well again in the Abram's reboot), but in the context of this movie, it should make their temporary victory over the Borg a hollow one. If the Borg have time travel, why haven't they used it since (and I'll admit I'm not up on Voyager or Enterprise history to know if they did after that) to go back in time and mess with human history? For that matter, why go back and assimilate Earth while humans have even the slightest chance of fighting back? Why not go back to prehistoric times and assimilate it then? Or during the Middle Ages? Yes, first contact with the Vulcans was a pivotal point in the history of the Trek universe...but if you alter human history centuries beforehand, they never even get to that point. Beyond that, how does the Enterprise get back to their own present time? They analyzed the Borg's chronometric particles to recreate the temporal vortex...and then as far as I know, it's promptly forgotten about in any Trek incarnation after that. I mean, come on: Data dies in Nemesis? "Recreate the temporal vortex!" Kirk dies from radiation poisoning? "Recreate the temporal vortex ERRR Khan blood!" Yeah. Sorry. Couldn't resist a dig on that deus ex machina in Star Trek Into Darkness, either, as that's another fictional universe altering discovery that will be completely ignored. Trek has tried to address the quandaries of discovering time travel in various mediums by creating the "Temporal Investigations" unit, which is all fine and good for people of normally high ethical standards like Starfleet and they promise never, ever to muck around in time again, but you're telling me the freaking Borg aren't going to? Or the Klingons? The Romulans? It's just something that's never really "realistically" addressed in most fictional universes once the gimmick of time travel is introduced. That would be an impossible genie to put back in the bottle.