Do you actually read the dialogue options or do you just look for the DS symbol and click? Because in my experience, especially when it comes to the Force User storylines, LS and DS choices tend to be incredibly simplistic and have nothing really to do with the end goals.
Sith DS choices tend to be less about ruthless quests for power and more 'lol I'm a psychopath, I'll get around to conquering the Empire after I go out of my way to set that puppy on fire and kick it around for a while.'. Similarly Jedi seem to be perfectly okay with the Republic going down in flames, as long as they can stand on the burning wreckage and give a longwinded speech about the Jedi Code and resisting the temptation of the Dark Side.
Some of the Republic-side quests (haven't played a Sith yet, but I guess I can comment on the Republic quests' LS/DS points) do seem to presume LS involves letting the Republic get weakened. One of the quests is trying to bring down a Senator who's getting very friendly with the Empire and trying to break the Republic's relations with the Jedi Order. So... you get DS points if you stick with the plan to have him ruined... Fine, likely due to the underhanded methods you have to use, I guess.
Some of the other DS options seem similar to the ones you describe for the Sith: E.g., being a psychopath and killing for the lulz. Others are more for greed or just power, though the LS choice isn't always a bad idea either. (There's one where you can let your toon be taken prisoner to free hostages.... and a number of the hostages arm themselves and come rescue your toon. I found that one cool.)
From what I've seen, Smugglers seem to be the only ones who can get away with pure LS/DS paths while still being believable characters/not being reduced to caricatures.
Hm. Yeah. The smuggler DS choices seems to be aimed at spreading fear/intimidation or keeping loose ends from causing problems, while the LS choices are for, hm, building a network, perhaps. Either will work, I guess. Perhaps it's trying to be a bit Machiavellian: To be Feared or Loved, though I'll have to continue playing to see if it also involves taking steps to make sure you're never Hated