Sojourn said:

Also, while we as the audience have the context of everything else that's happening to every character, the characters themselves do not -- other than knowing that Locke is back and seems to be different, how are they supposed to know that he's considered "evil incarnate"? He's actually been somewhat charming and reasonable in many of his conversations with the characters now aligning (or considering aligning) themselves with him.

The problem is that EVERYONE KNOWS HE'S DEAD. Sawyer said so, and Claire knows its not Locke. He sees Locke, doesn't care that he was dead, follows him to a cave where he shows him names on a wall and now he'll follow him to the ends of the Island. Even if they don't know he's evil incarnate, they should at least have a clue that maybe this dead guy might be up to no good.