1x12 faith is a great episode because it's right after 1x11 scarecrow where sam chooses dean over revenge for the first time, and then we proceed to watch him not give a shit about not just one innocent person dying to save dean's life, but two people dying to save dean's life.
because sure, sam has plenty of deniability for the first victim of sue ann and her reaper—he had no idea how roy worked and that sue ann was killing people behind the scenes with roy as the face of her operation. guy dies, dean is guilty, sam is guilty because dean is upset. okay, sure.
but then they figure out exactly what sue ann is doing, and sam is acting fully informed. and he has the opportunity to set things right: save the innocent layla by rectifying his mistake and trading dean's life for hers. dean isn't supposed to be alive, and he's made it very, very obvious that he would rather die in layla's place—he had accepted his death, tried to get sam to accept it too, wallowed in guilt once they found out what was going on. sam has dean's blessing, he knows what dean wants, and when sam goes to stop sue ann and discovers that dean has the target on his back, he's given the perfect opportunity to put the cosmic order back in place and save an innocent girl's life to make up for the one he accidentally took.
and then he just doesn't. he knowingly and willingly sends layla to her death because he can't let dean die. he chose dean over her and he was okay with that. and this illustrates exactly the point scarecrow was making: choosing family, choosing the collective, choosing dean, will always require sacrificial offerings to keep each other alive. they will be forced over and over again to choose between innocent lives and each other, and they will happily offer up those outsiders to the stone just to keep each other alive.
sam had the chance to put things right, to rectify his mistake—and he just did it all over again instead, without even hesitating.