"Wh..." Klaus is frowning and about to ask what she is talking about, but there's really only one thing, and he trails off.

"You wouldn't," he confirms, after a moment. "Well, it would likely make you angry more than anything else. And you'd probably be dead within a week, in these circumstances."

He doesn't trust that she wouldn't kill, if she did it. It's the most pragmatic reason why he doesn't want her to do it, the one that doesn't make his blood boil, but it's what he chooses to focus on, because it is her choice, and he understands the need. He tried it, too.