I'm having hard time believing that Sayid, Claire, and Sawyer would actually join the Dark Side of their own free will. Yes, I know that they've all lost the person they cared for most in the world. Yes, I know that they blame people on the other team (Sayid blames Ben, Claire blames Kate, Sawyer blames Jack) but would they seriously trade-in their immortal soul?
My wife reminded me that Claire and Sayid have been affected by the Man in Black and maybe they're not fully in control of their actions- maybe they're not all there, really. I guess something like that is
1) required to make me believe that these people would make these kind of decisions
2) LAAAAAAAAAAAAAAAAAAAAAAAAAAAAME.
It's just like any most other characters that turns to the Dark Side long term- The moment they actually turn the corner rings a little false.
Especially Sawyer. He's been such a good egg- responsilbe leader of the 1974 Losties for 3 years. The "badboy" image he tried so hard to cultivate after the crash (and probably before) was a charade and once Kate and others forced him to reveal his true noble, yet tortured and a bit misguided, character... he's been one of the good guys. Yes, I know Juliet's death would have been hard on him. Yes, I get that he, in a moment of rage, would take it out on Jack. But I can't see him joining MIB, or taking more permanent action against Jack and the "White team".
(Also, when Dogan told Sayid that his scale had tipped to "evil" it reminded me of the Treehouse of Horror episode where the Crusty doll tries to kill Homer because it was accidentally switched from "good" to "evil.")