^The sad fact is, a shuttlecraft could destroy the entire habitable surface of a planet -- all it'd have to do is use its impulse engines to accelerate to relativistic speed and then crash into the planet. The kinetic energy of the impact would be comparable to that of the asteroid that killed the dinosaurs.
Alternatively, any ship with a tractor beam could divert an asteroid onto a collision course with a planet and have the same effect. The disturbing thing about space travel is how easy it would be to destroy an entire planet if one were so motivated. Heck, a single drunk driver with an impulse engine could wipe out a civilization.
And this is one thing Trek usually gets wrong, because any planet in a spacefaring civilization would need one hell of a good orbital defense network to guard against such cataclysms, accidental or intentional. And yet there's rarely any mention of Earth or any other Federation world having any kind of orbital defenses, except in TMP (where V'Ger got the shutdown codes for the defense grid from the Enterprise
computer) and ST'09 (when Nero tortured the codes out of Pike).