If you had been someone who helped people in life, though, Sam reasoned, would dying really change that about you, even if you did come back with an incurable thirst? Had Sam stopped wanting to help people, even when he was addicted to demon blood? He knew now that the ends didn't really justify the means, but it was less of a stretch for him to accept the fact that a good person, even a hunter, could get turned, and yet try to stay true to who they had been before.
After all, Dean might be human, but he was no less a predator. He just happened to hunt other predators.
Sam shrugged. "One minute, they were making eyes at each other, the next minute, they weren't, and Harry was passed out on the floor. But of course the end is nigh. I mean, when is it ever not?"