[throwatdem12311]

There is the Maquis which are basically insurrectionists/terrorists and Starfleet also has Section 31 for doing wet work.

Sisko poisoned a planet’s atmosphere, allowed political assassinations and even Picard did things that could be considered questionable once or twice, even Kirk.

Earth is peaceful because well…in a show about exploring space nobody really wants to see conflicts on Earth (there are a few exceptions where it worked though). And they have enough big guns and secret assassins to keep up appearances.

[Melatonic]

Earth is peaceful because they went through the horrors of WWIII already