I want to talk about what happened between these two scenes, because I think it’s really interesting.
5x09: Elena’s initial response is pretty straightforward. Shock, horror, fury, betrayal. And yes, despite what she says, judgment. Not just because he was being murdery, but also because he was being something he usually isn’t: calculated in his ruthlessness. Cold-blooded. Early S1 excepted, usually when he commits atrocities it’s in impulsive hot blood or for the sake of convenience, or with a clear purpose. She doesn’t have to like those things, but she can usually understand them. It looks to me like she can’t wrap her head around why he would do something like this.
5x10: Cut to an episode later. A few important things happened between these two scenes. First, she was thrust into the situation that prompted Damon’s anti-Whitmore vendetta. I think it’s possible that an afternoon on Creepy Prof #2’s table made Damon’s experience more tangible to her, at least a little.
More significantly, though, I think it gave her time to cool off and for her tribalism and abandonment issues to work through the problem. When he asks her why she hasn’t run for the hills, she says: “Because I love you. Because I chose you, and I stand by my choice.” Damon’s a member of her tribe, and that means she’s supposed to accept him for who he is–she doesn’t have to agree with him, but she also doesn’t want to be the kind of person who would judge someone she loves. I think there might also be an element of obligation here, too: “I stand by my choice” sounds a little like she doesn’t want to flip flop anymore. She made her bed with eyes wide open, and now she thinks she should lie in it. (Literally. I think she’s lying to herself and to him when she says she doesn’t judge him, and I think it’s fascinating.)
As for her next two statements–you can actually see her strategic empathy kick in with the “Stop acting like I’m perfect” line, which is right after he says he’s going to leave her. More than anything, she’s casting around for anything to say to stop him from doing it, because that’s what Elena does: her desperation takes over and she maneuvers to avoid abandonment. She hears him saying he’s a bad person and therefore bad for her, and she counters him by reminding him she’s bad too, and so he shouldn’t feel bad about being bad. I don’t think she had to try very hard to think of this response, because I’m sure it was already on her mind while she was digesting Damon’s recent recreational activities. Who is she to judge, with a kill list of her own? Another thing that was already on her mind: what kind of person would judge somebody’s coping mechanisms after they endured years of trauma? She hears him saying he feels judged, and she tries to talk him out of it to make him stay.
…And it doesn’t work. She’s usually better than this. She’s a little off her game, manipulation-wise. Maybe because she was caught off guard by his recent actions and isn’t trusting her instincts as much. Maybe because she’s suppressing some things she doesn’t want to feel. Maybe she’s just tired, which is probably part of it. Either way, I’ll be interested to see how this is dealt with in the upcoming episodes. (Once Elena deals with the slightly more important matter of getting her body back. First things first.)