I'm guessing it's a contextual thing. The Force is life, but one of the primary motivators to maintaining the existence of a species is inherently Dark Side? I don't think so. I think it's more a matter of it being DS when your passion overrules your greater sense of balance, or when it sways you from a more inherently LS path (which probably still doesn't explain the no-DS-for-snogging-Nadia thing).
As far as I know, for the Jedi of this era, it's not so much about sex as it is attachments - Jedi aren't supposed to form them, as they supposedly can lead to stronger emotions/feelings toward one person, and that can lead to the Dark Side.
Remember, there's that one mission on Tython where choosing to hide the fact that two padawans are in a relationship gets you DS points. And on an JK mission, saying you care very strongly for Kira gets you DS points, though it also gets you affection with Kira, so I'd say it's an even trade.
Totally playing my JK as grey because I know I'll be getting DS points for romancing Kira, assuming she's SGR-able.
Also, the new Q&A thread is now open
. Yes, I know the odds of getting an answer about SGRs there seems slightly less than becoming a millionaire just by going to Las Vegas, but if you don't have any other crucial question to ask, might as well ask about SGRs. Can't have BioWare forgetting we're here, can we?
(Crazy SWTOR player channel turned to mute.)
Please don't take this the wrong way, but I would totally hug you for that if I could.