My question is....why the HELL do you care what other people do? It doesn't effect your choice except for in the cinematic....YOU still get the full LS/DS point increase based on YOUR individual choice. Personally, I'm playing my SA entire DS. I don't care what it is, if it's dark, I'm taking it! Most of the time because I just like the option better anyway.
As a Sith though, I feel like I get the opportunity to be the most ruthless, scheming, disgusting bastard I can possibly be, and that's what I want to do with my SA. The majority of the time, it fits with what a SA SHOULD be anyway.
So, when you start paying everyone elses' subscription, you can decide how they make their choices. But until then, enjoy your own, and do what you want. The minute you stop worrying about everyone else, is the minute you'll start REALLY having a blast with the game.