I think Parvati played both idols because that was the super power play that couldn't miss. First, Parvati dropped off the pole guaranteing that Danielle would be safe. Russell was safe because the heros thought he had flipped (despite Sandra telling Rupert the truth). Parvati knew shge was safe when she saw through Amanda's lame story.
So -- give one idol to Sandra and the other to Jerry, and she's got all of her bases covered. JT goes home.
But for the long run, it could backfire. Russell now sees that he can't trust her and he may join the Heros to vote her out. Sandra will go her own way and not feel any gratitude to Parvati anyway. For some reason, no one can stand Parvoti except Danielle.
Or -- if everyone keeps taliking about a girls' alliance, maybe the girls will wake up and say, hey, let's have a girls' alliance! They better hurry, though, before Russell finds another two or three immunity idols.
Seanibu's view of Survivor as reflecting the moral choices that we have in real life -- I think there is another way to look at it. When you sign up to play Survivor, you are signing up to play a make-believe game of lying, cheating and scheming. If you don't want to lie, cheat and scheme, Survivor is not the game for you. Whoever lies, cheats and schemes the best, wins. The people who get out-lied, out-cheated and our-schemed should acknowledge that the other guy played the best and deserves to win.
Unfortunately, human nature doesn't cooperate. When someone tricks you and votes you off, you get mad and irrationally vote to give the money to some sweetie-pie girl or nice guy who didn't lift a finger the whole game but just rode of someone's coattails. (JMO.)