I suppose there's a need to take artistic license and world management into account. I mean if the devs approached it from a direct viewpoint of Passion = DS for everyone then they'd need to comb through every bit of dialogue and go, 'Is that passionate? DARK SIDE POINTS FOR YOU!' and everyone would be running about throwing Force Lightning at people, choking accountants and having little Sith-babies all over the place.
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).
Incidentally, you figured what I meant anyway, but I meant dark side points, not negative affection....I have no idea why I typed that, must have been tired.
But yes, that was what I was trying to say...it's all about the context. I haven't played a JK yet, but the Consular takes a fairly guarded/cautious route with the relationship and it feels less about passion and more about bonding, and challenging the Jedi code's stance on relationships. There's certainly talk about the danger of attachment and all that, though I can't remember the specifics. But you're right,, it seems like cherry picking to some degree.