Its understandable for Chris to cast him away, especially since its never made clear if Chris even loved Sam in the first place.

Pat's case is also easily understandable. You cant expect getting something for nothing, and while the price is shocking, thats what it is.

Alex comes in at second worst. A friend should have done a favor for a friend, but that's not why I blame him. He took in only Sam's side of the story, which do to his evident psychopathic nature, I assume was full of lies and half truths. While this is the most violent act in the story, I wont label him the worst because his intent was honorable.

Sam is a monster from my perspective. I may be reading too much into what isn't there, but from his twisted enjoyment I assume there was some intent to get alex to behave that way.

Assumimg there was no trickery or half truths then alex and sam are tied. Since it is clear that the outcome is what Sam wanted.