This has always been the thing I've been most puzzled about in SAGA. Why is Force Grip (more commonly known as Force CHOKE...) not a dark side power? One could argue it's the poster boy for a dark side power in the original trilogy. The Emperor uses Force Lightning once, but Darth Vader keeps choking people left and right. Sure, it's dark sidey to use the Force in a violent manner, to harm "innocent" officers, but I would think that the power itself is drenched in the dark side. So, even if you used it in self-defense, I would absolutely deal you a dark side point right away.
So this power is a rarity for me: it's something that I houserule in SAGA. Generally, SAGA is so well designed that I very rarely houserule anything. There's nothing mechanically wrong in Force Grip, but I seem to have a different philosophy here.
In the films, next there's the matter of Luke entering Jabba's palace and seemingly Force choking the gamorrean guards. Is that the reason it's not a dark side power? I always thought that Luke IS actually using a dark side power here, to help the audience understand that he's not THAT different from his father, that he does have all the same potential for darkness (even if he will choose another path in the end). So yeah, a dark side point to Luke from me!
A final matter to consider is the nature of the power itself. What does it do, really? It's written in SAGA as a purely telekinetic thing, and even has the telekinetic label in the errata. Ok, you are just exerting some pressure on someone's body, bit like Force Slam? I guess it's possible to think of it that way... but it always seemed to me to be something more. A power to choke the LIFE out of someone, even if used just in moderation and non-lethally. The dark side of the Force sucking not just the air out of your lungs, but the life out of your body!
So, what do you think? A clever telekinetic battle trick, or summoning forth the power of darkness itself?
I have no problem with a GM house-ruling that Force Grip is a dark side force power. I agree with pretty much everything you mentioned. In the previous version of Saga Edition which was called the Revised Core Rulebook, Force Grip was a dark side force power. Using it earned you an automatic Darkside Point.
What makes a Force power "Dark" often seems to simply be a matter of, "Did the bad guy use this? If yes, then it's darkside." If we apply that to Force Grip, then it should definitely be a dark side power.