Violent Content
It's fair to say that the casualty count of Into Darkness is far lower than that of its predecessor, 2009's Star Trek. Of course, we must keep in mind that in that remake director J.J. Abrams blew up an entire planet. This go-round he only has a massive starship plow through a major city, keeping fatalities down to the five- or six-digit range.
Into Darkness is a tale about terrorism to some extent. Harrison procures the help of a Federation employee to blow up a building, killing 42 people. He shoots up another building full of Starfleet officers, murdering or wounding several more. His destruction of what appears to be much of futuristic San Francisco is his version of 9/11 (only many times worse). And if that isn't enough, this genetically enhanced villain has the strength to crush a man's skull with his hands—an assassination technique he performs on one unlucky victim (offscreen, thankfully).
But even discounting Harrison's fearsome scythe, the movie is plenty violent. Photon torpedoes detonate to brain-frying effect. We see phaser fights and fisticuffs, leaving folks bloody and bruised. People are sucked out of spaceships through open airlocks and gaping gashes blasted through starship hulls. Heroes are threatened by lava, Klingon blades and space debris. They hang from dizzying heights and succumb to radiation poisoning. A daughter slaps a father. A leg is broken with a sickening snap. Spock wrenches a guy's arm. We see part of a smoldering body.
The future, clearly, is not a more gentle, peaceful time.
Crude or Profane Language
Three s-words punctuate flurries of other profanities, including "a‑‑" (said five or six times), "b‑‑ch" (three or four), "b‑‑tard" (five or six), "d‑‑n" (a dozen), "h‑‑‑" (another dozen), and "p‑‑‑" and "bloody" (once each). God's name is misused close to half-a-dozen times.